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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 2 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Net of Valuation Allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total deferred tax assets, net of allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted Average Exercise Price [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income, Noncurrent</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares Authorized</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasicAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Basic [Abstract]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Product and Service [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ProductOrServiceAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Product and Service</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockVotingRights_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, voting rights</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockVotingRights_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Voting Rights</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Interest Rate, Stated Percentage</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Maximum interest rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountingStandardsUpdate202309Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">ASU - 2023-09</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue from Contract with Customer [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ContractualObligation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contractual Obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ContractualObligation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contractual obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ContractualObligation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ContractualObligation_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total debt obligations, including final payment fee (Face Value)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Accrued Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantIssuanceExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrant issuance expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantIssuanceExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrant issuance expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issuances</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Information</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash and Cash Equivalents, at Carrying Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportingUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Reporting Units</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportingUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of reporting units</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsidiary, Sale of Stock [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Arrangement, Contract to Perform for Others, Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementStrategyAndGovernanceAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management, Strategy, and Governance [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issued (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementPositionsOrCommitteesResponsibleReportToBoardFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskBoardOfDirectorsOversightTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Board of Directors Oversight [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross increase &#8211; current-period tax positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Right-of-use assets acquired by assuming operating lease liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Right-of-Use Asset Obtained in Exchange for Operating Lease Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Resulting fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointFiveZeroMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Closing Stock Price Not Below Zero Point Five Zero [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointFiveZeroMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing Stock Price Not Below Zero Point Five Zero.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand twenty two distribution agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Two Distribution Agreement [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ScheduleOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of right of use assets and lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ScheduleOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Right Of Use Assets And Lease Liabilities Table [Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of treasury stock</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant Revenue Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue from Contract with Customer [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrant [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LoremVascularPteLtdMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Lorem Vascular, Pte. Ltd.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">FIN48, Percent</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidDuringPeriodForAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid during period for:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CongressionallyDirectedMedicalResearchProgramsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Congressionally Directed Medical Research Programs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CongressionallyDirectedMedicalResearchProgramsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Congressionally Directed Medical Research Programs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CongressionallyDirectedMedicalResearchProgramsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Congressionally directed medical research programs.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrant Liability Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrant liability noncurrent.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Tax at statutory rate: Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand eighteen rights offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Eighteen Rights Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandEighteenRightsOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2018 Rights Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementThirdPartyEngagedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Third Party Engaged [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentsIncorporatedByReferenceTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Documents Incorporated by Reference [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandAndTwentyTwoPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Two thousand and twenty two purchase agreement.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Goodwill, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Goodwill, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageExpectedDividend_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Weighted Average Expected Dividend</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageExpectedDividend_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dividend yield assumed</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income tax rate reconciliation, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Income, Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock (at cost, 78,559 shars as of December 31, 2023)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonValue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury stock (at cost), 258,425 shares as of December 31, 2025 and 2024, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Jurisdiction [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxAuthorityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Tax Authority</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of intangible assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and Cash Equivalents, and Restricted Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Preferred stock dividend rate percentage eliminated date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock Dividend Rate Percentage Eliminated Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreferredStockDividendRatePercentageEliminatedDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series A 3.6% Convertible preferred stock eliminated date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScheduleOfValuationAndQualifyingAccountsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScheduleOfValuationAndQualifyingAccountsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Statement Schedules</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued, Shares, Share-Based Payment Arrangement, Forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cancellation of common stock (in Shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialSubscriptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Initial Subscription [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialSubscriptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Initial Subscription.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RightsRelatedToDistributionOfAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rights related to distribution of assets</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RightsRelatedToDistributionOfAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Rights related to distribution of assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SPEAWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">SPEA Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SPEAWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">SPEA Warrants.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfGrantProceedsWithInterestNotExceedAnnually_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of grant proceeds with interest not exceed annually</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodValueReclassificationOfWarrantsToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification of warrants to equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Property, Plant and Equipment</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputRiskFreeInterestRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Risk Free Interest Rate [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeOfWarrantsForNotesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exchange Of Warrants For Notes Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeOfWarrantsForNotesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exchange of warrants for notes payable.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesPurchasedOptionsPricePolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Premium on Purchased Options [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesPurchasedOptionsPricePolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available-for-Sale Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Repayments of Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Repayments of Long-Term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Principal payments of term loan obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SharesIssuedSharesShareBasedPaymentArrangementForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued, Shares, Share Based Payment Arrangement, Forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SharesIssuedSharesShareBasedPaymentArrangementForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of shares (or other type of equity) forfeited during the period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SharesIssuedSharesShareBasedPaymentArrangementForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cancellation of common stock (in Shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfEquity_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of treasury stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Purchase of treasury stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for Repurchase of Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for Repurchase of Equity, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance as of December 31, 2024 (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance as of December 31, 2025 (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnDispositionOfAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnDispositionOfAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Gain on sale of assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssued1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock issued in payment for in process research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssued1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred Financing Costs and Other Debt-Related Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumObligationUnderSingleRegularPurchase_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Obligation Under Single Regular Purchase</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumObligationUnderSingleRegularPurchase_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum obligation under single regular purchase.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock, sales, available for issuance.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Sales Available For Issuance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockSalesAvailableForIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining availability under financing facility</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DeferredTaxAssetsValuationAllowances_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deferred tax assets valuation allowances.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DeferredTaxAssetsValuationAllowances_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets Valuation Allowances</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DeferredTaxAssetsValuationAllowances_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrants Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrants Policy.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2030</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Change in Fair Value of Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DomesticCountryMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Domestic Tax Jurisdiction [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DomesticCountryMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassified to equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Reclassified To Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value measurement with unobservable inputs reconciliation recurring basis liability reclassified to equity.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Reclassification to equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrantsShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of pre-funded warrants (in Shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrantsShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exercise Of Pre-funded Warrants Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrantsShares_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exercise of pre-funded warrants shares.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross increases - tax positions in prior period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LicenseAgreementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">License agreement abstract.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LicenseAgreementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TermLoanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Second amendment to the amended and restated loan and security agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TermLoanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Term Loan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TermLoanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term Loan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders' equity (deficit):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SupportLetterParticipationRightsPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Support Letter Participation Rights Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SupportLetterParticipationRightsPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Support letter participation rights period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SupportLetterParticipationRightsPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Support letter participation rights period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series A convertible preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series A Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series A Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings (Accumulated Deficit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated deficit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Retained Earnings (Accumulated Deficit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-Based Compensation Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IssuanceOfCommonStockPrefundedWarrantsAndWarrantsForDebtRepayment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock, pre-funded warrants and warrants for debt repayment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IssuanceOfCommonStockPrefundedWarrantsAndWarrantsForDebtRepayment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Issuance Of Common Stock, Prefunded Warrants And Warrants For Debt Repayment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IssuanceOfCommonStockPrefundedWarrantsAndWarrantsForDebtRepayment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Issuance of common stock, prefunded warrants and warrants for debt repayment.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsidiary or Equity Method Investee, Sale of Stock, Type [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Amount, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of cross border tax laws, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantsReceivableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Grants Receivable, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantsReceivableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointSevenFiveMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Closing Stock Price Not Below Zero Point Seven Five [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointSevenFiveMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing Stock Price Not Below Zero Point Seven Five.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Well-known Seasoned Issuer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Well-known Seasoned Issuer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cancelled/forfeited (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at December 31, 2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WarrantsAndRightsOutstandingMeasurementInput_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrants and Rights Outstanding, Measurement Input</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WarrantsAndRightsOutstandingMeasurementInput_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant liability, Measurement input</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based Compensation</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan [Table]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax at statutory rate: Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Tax at statutory rate: Amount</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of securities called by warrant or right</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Policy [Policy Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeptemberTwoThousandAndTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">September two thousand and twenty two distribution agreement.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeptemberTwoThousandAndTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">September 2022 Distribution Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Operating Activity, Including Discontinued Operation</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillPeriodIncreaseDecrease_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Goodwill, Period Increase (Decrease), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumValueOfSharesToBeIssuedUnderAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum value of shares to be issued under agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumValueOfSharesToBeIssuedUnderAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Value of Shares to be Issued Under Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumValueOfSharesToBeIssuedUnderAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Maximum value of shares to be issued under agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskRoleOfManagementTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Role of Management [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan, Employer Discretionary Contribution Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discretionary or matching contributions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less accumulated depreciation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Arrangement, Contract to Perform for Others, Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development Arrangement, Contract to Perform for Others, Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Address Line One</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilities_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Total deferred tax liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Tax Liabilities, Gross, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in accounting principle, accounting standards update, immaterial effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateImmaterialEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted-average Assumptions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax, Policy [Policy Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskMateriallyAffectedOrReasonablyLikelyToMateriallyAffectRegistrantFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfProceedsToRepayPurchasersFromCapitalRaised_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Proceeds to Repay Purchasers from Capital Raised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfProceedsToRepayPurchasersFromCapitalRaised_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of proceeds to repay purchasers from capital raised.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveSecuritiesPurchaseAndExchangeAgreementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">February Two Thousand Twenty Five Securities Purchase and Exchange Agreements [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveSecuritiesPurchaseAndExchangeAgreementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">February two thousand twenty five securities purchase and exchange agreements.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveSecuritiesPurchaseAndExchangeAgreementsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">February 2025 SPEA Agreements [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAAndBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">March two thousand twenty five series A and B warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAAndBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">March 2025 Series A and B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating lease right-use-of assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right-of-use assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RedemptionOfShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Redemption of Short-Term Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RedemptionOfShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Redemption of Short-Term Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RedemptionOfShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from redemption of short-term investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total deferred tax assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Canaccord Genuity L L C Member</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Canaccord Genuity L L C [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Canaccord Genuity LLC [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CanaccordGenuityLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Canaccord Genuity LLC [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskBoardCommitteeOrSubcommitteeResponsibleForOversightTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PershingCreditFacilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pershing Credit Facility [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PershingCreditFacilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pershing Credit Facility [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PershingCreditFacilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Pershing Credit Facility.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Charlottesville</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Charlottesville [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CharlottesvilleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Charlottesville [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightExpirationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right Expiration Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightExpirationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Class of warrant or right expiration period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightExpirationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expiration period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedVacationAndCompensationCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued vacation and compensation, current.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedVacationAndCompensationCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Vacation And Compensation Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedVacationAndCompensationCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued vacation and compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Reconciliation Nondeductible Expense Permanent Differences Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Income tax reconciliation nondeductible expense permanent differences amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Permanent differences, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Permanent differences, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill and Intangible Assets, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exchange Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exchange notes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exchange Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCreditFacilityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Line of Credit Facility [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Contractual Maturities of Available-for-sale Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments, Debt and Equity Securities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskProcessForInformingBoardCommitteeOrSubcommitteeResponsibleForOversightTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrimeRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Prime Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrimeRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prime Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OperatingLossCarryforwardsExpirationDates1_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">The expiration date of each operating loss carryforward included in total operating loss carryforwards, or the applicable range of such expiration dates.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OperatingLossCarryforwardsExpirationDates1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards Expiration Dates1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OperatingLossCarryforwardsExpirationDates1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net operating loss carryforwards, Expire date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net increase (decrease) in cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Fair value loss on warrant liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Change in fair value of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in fair value of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAdjustmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in fair value of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dilutive common shares excluded from the calculations of diluted loss per share (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Repurchased and Retired During Period, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares returned and cancelled</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermDebtTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Debt [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermDebtTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Line of Credit Facility</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License Agreements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure of accounting policy for license agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LicenseAgreementDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">License Agreement Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentOfferingDate1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Offering Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentOfferingDate1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Origination date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Issuance of Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from issuance of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PrefundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Prefunded Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PrefundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Prefunded Warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction in the carrying amount of operating lease right-of-use assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Right-of-Use Asset, Periodic Reduction</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockIssuedForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock issued for research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockIssuedForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock Issued for Research and Development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommonStockIssuedForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Common stock issued for research and development.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OptionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Options.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OptionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Options [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OptionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Outstanding Stock Options [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance as of December 31, 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Securities, available-for-sale, amortized cost and fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortized Cost</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanDisclosureLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan Disclosure [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAndLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Components of Deferred Tax Assets and Liabilities [Abstract]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Estimated Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregatePurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Aggregate Purchase Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregatePurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate purchase price.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregatePurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate purchase price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodValueExerciseOrExchangeOfSeriesAAndBWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise or exchange of March 2025 Series A and B Warrants</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodValueExerciseOrExchangeOfSeriesAAndBWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period value exercise or exchange of Series A and B warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFinStmtErrorCorrectionFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Financial Statement Error Correction [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PotentialCashPayment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Potential Cash Payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PotentialCashPayment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Potential cash payment.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PotentialCashPayment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Potential cash payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnpaidLiabilityToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unpaid liability to investors pursuant to Letter Agreement</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnpaidLiabilityToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Unpaid liability to investors pursuant to letter agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherPrepaidExpenseCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Prepaid Expense, Current</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Other_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Other_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Other_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ProfessionalExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Professional Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ProfessionalExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Professional expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementInputsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement and Measurement Inputs, Recurring and Nonrecurring [Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketableSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Marketable Securities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing expense.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingExpense_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Financing expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SeriesFPreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series F Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Long-Term Debt Instruments [Table]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ModificationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Modification Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ModificationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Modification period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DistributionTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Distribution Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LitigationCaseTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Case [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LitigationCaseTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Litigation Case</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LincolnParkCapitalFundLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Lincoln park capital fund, LLC.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LincolnParkCapitalFundLLCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lincoln Park Capital Fund, LLC [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, by Balance Sheet Grouping [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Unvested as of December 31, 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Unvested as of December 31, 2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalAcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Accelerated Purchase Price Per share Threshold Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalAcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional accelerated purchase price per share threshold percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalAcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional accelerated purchase price per share threshold percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConsiderationPaidToPreferredStockHolders_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consideration paid to preferred stock holders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConsiderationPaidToPreferredStockHolders_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consideration Paid To Preferred Stock Holders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConsiderationPaidToPreferredStockHolders_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consideration paid to preferred stock holders.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares outstanding (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Preferred Stock, Shares Outstanding, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Preferred Stock, Shares Outstanding, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpensePolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Expense, Policy [Policy Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common stock capital shares reserved for future issuance</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationByCategoryOfItemPurchasedAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Unconditional Purchase Obligation by Category of Item Purchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Warrant or Right</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncreaseDecreaseInGrantReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Grant Receivable</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncreaseDecreaseInGrantReceivable_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Grant receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for Royalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRoyalties_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">License fee payment in cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Value, Stock Options Exercised</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PeriodExercisableFromTheDateOfIssuance_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to the period exercisable from the date of issuance.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IssuanceOfCommonStockSharesPrefundedWarrantsAndWarrantsForDebtRepayment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock, pre-funded warrants and warrants for debt repayment (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LiabilityToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability to Investors Pursuant to Letter Agreement</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConsecutiveBusinessDays_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consecutive business days.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConsecutiveBusinessDays_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consecutive business days</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">May Two Thousand Twenty Four Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">May Two Thousand Twenty Four Series B Warrants Member.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">May 2024 Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract effective date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract Effective Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract effective date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets, Noncurrent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputExpectedTermMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected Term [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputExpectedTermMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Expected Term [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfRevenueExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue, Product and Service [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock option vesting percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable and Accrued Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts Payable and Accrued Expenses [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">May Two Thousand Twenty Four Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">May two thousand twenty four purchase agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwoThousandTwentyFourPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">May 2024 Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointOneZeroMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Closing Stock Price Not Below Zero Point One Zero [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingStockPriceNotBelowZeroPointOneZeroMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing Stock Price Not Below Zero Point One Zero.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">State and Local Jurisdiction [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StateAndLocalJurisdictionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Cost by Plan [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Share-Based Compensation Recognized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of Series B Warrants from May 2024 PIPE (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period shares warrants exercise(shares).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Warrants Exercise Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrant liability.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrant Liability [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantLiabilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant Liability [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SingleStockFutureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Single-Stock Future [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SingleStockFutureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Single Regular Purchase [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance, Treasury (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance, Treasury (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Black-Scholes-Merton option valuation model based on weighted-average assumptions [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and Cash Equivalents [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum beneficial ownership percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Beneficial Ownership Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum beneficial ownership percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,952 shares issued and outstanding as of December 31, 2025 and 2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Maturity Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentMaturityDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maturity date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Income taxes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Taxes [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Current [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current assets:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Unconditional Purchase Obligation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amortization of Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 3 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 3 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentShares_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Initial commitment shares.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Initial Commitment Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial commitment shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityModificationAndExtinguishment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Modification and Extinguishment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityModificationAndExtinguishment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value measurement with unobservable inputs reconciliation recurring basis liability modification and extinguishment.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityModificationAndExtinguishment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Modification and extinguishment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Financial Assets Measured at Fair Value on Recurring Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets Measured on Recurring Basis [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities, Current [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Repurchased and Retired During Period, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Paid purchasers to returened shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Paid purchasers to returned shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares, Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Loss Carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax loss carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable and Accrued Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitment fee.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitment Fee [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CommitmentFeeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitment Fee [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and contingencies (Note 7)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Offering Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Offering costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Offering cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Offering expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Unvested as of December 31, 2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Unvested as of December 31, 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">General and Administrative Expense [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">General and Administrative [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFivePrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">March Two Thousand Twenty Five Private Placement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFivePrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">March Two Thousand Twenty Five Private Placement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFivePrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">March 2025 Private Placement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Present value of obligations under leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorFirmId_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Auditor Firm ID</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorFirmId_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Auditor Firm ID</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred grant liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Basis Spread on Variable Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis variable rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Dividend Rate, Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible preferred stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Commitment Fee</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional commitment fee.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional commitment fee paid in cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractTerminationDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contract termination date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractTerminationDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contract Termination Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ContractTerminationDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Contract termination date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ScheduleOfOperatingAndFinancingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of operating and financing lease liability maturity.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ScheduleOfOperatingAndFinancingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Operating And Financing Lease Liability Maturity Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ScheduleOfOperatingAndFinancingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Future Minimum Annual Lease Payments under Operating and Financing Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsAndShortTermInvestmentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, and Short-Term Investment [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsAndShortTermInvestmentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-Term Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RemeasurementOfWarrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Remeasurement of Warrant Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RemeasurementOfWarrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Remeasurement of warrant liability.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RemeasurementOfWarrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remeasurement of warrant liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeLeaseDescriptionTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Lease, Description [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCreditFacilityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Line of Credit Facility [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in valuation allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in valuation allowance: Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementPositionsOrCommitteesResponsibleTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Positions or Committees Responsible [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Weighted Average Number of Shares Outstanding, Basic, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average shares of common stock outstanding - basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Weighted average number of shares of common stock outstanding - basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LGOnePropertyOwnerLPMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">LG One Property Owner LP [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LGOnePropertyOwnerLPMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Lg one property owner lp.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementScenarioAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesRestrictedStockUnitVesting_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Restricted Stock Unit Vesting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesRestrictedStockUnitVesting_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock Issued During Period, Shares, Restricted Stock Unit Vesting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesRestrictedStockUnitVesting_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock unit vesting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for amounts included in the measurement of lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For Amounts Included In Measurement Of Lease Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total cash paid for amounts included in the measurement of lease liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNetOperatingLossCarryforwardsAvailableForOffsettingAgainstFutureTaxableIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of net operating loss carryforwards available for offsetting against future taxable income.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNetOperatingLossCarryforwardsAvailableForOffsettingAgainstFutureTaxableIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Net Operating Loss Carryforwards Available For Offsetting Against Future Taxable Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNetOperatingLossCarryforwardsAvailableForOffsettingAgainstFutureTaxableIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of federal net operating losses used to offset of future taxable income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at December 31, 2023</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingExpenseInformationUsedByCodmDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, Expense Information Used by CODM, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reconciliation of Income Tax Benefit At U.S. Federal Statutory Rate to Provision for Income Taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Grant funding term.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Grant Funding Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant funding term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskProcessForInformingManagementOrCommitteesResponsibleTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfInvestorLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction of additional paid-in-capital of investor liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfInvestorLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reduction of Additional Paid-in-Capital of Investor Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfInvestorLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Reduction of additional paid-in-capital of investor liability.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfPrivatePlacement_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Issuance of Private Placement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfPrivatePlacement_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from private placement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Events</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">APIC, Share-Based Payment Arrangement, Increase for Cost Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">APIC, Share-Based Payment Arrangement, Increase for Cost Recognition, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableRateDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsInProcessResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Asset, In-Process Research and Development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsInProcessResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Capitalized R&amp;D</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in valuation allowance: Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in valuation allowance: Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total stockholders' equity (deficit)</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Stockholders' Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Issued, Value, Share-Based Payment Arrangement, Forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cancellation of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationForfeited_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cancellation of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Use of Estimates, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OverAllotmentOptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Over-Allotment Option [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Address Line Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine2_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LetterAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Letter Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LetterAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Letter Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Options [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentageByElectionOfHolder_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Beneficial Ownership Percentage By Election Of Holder</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentageByElectionOfHolder_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum beneficial ownership percentage by election of holder.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumBeneficialOwnershipPercentageByElectionOfHolder_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum beneficial ownership percentage by election of holder</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized Tax Benefits Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InProcessResearchAndDevelopmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">In Process Research and Development [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Plan Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PlanNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Plan Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Initial commitment fee.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Initial Commitment Fee</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Initial commitment fee paid in cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InitialCommitmentFee_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Initial commitment fee</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Excess of fair value of instruments issued over cash received</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Settlement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationCategoryDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation, Category [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateRepurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate repurchase price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateRepurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Aggregate Repurchase Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateRepurchasePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate repurchase price.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateExpenseIncludingFeeAndDisbursementExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Aggregate expense including fee and disbursement expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateExpenseIncludingFeeAndDisbursementExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Aggregate Expense Including Fee and Disbursement Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AggregateExpenseIncludingFeeAndDisbursementExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Reimburse of fee and disbursements expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditFacilityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Facility [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskMateriallyAffectedOrReasonablyLikelyToMateriallyAffectRegistrantTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Impairment, Long-Lived Asset, Held-for-Use</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Impairment, Long-Lived Asset, Held-for-Use, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested and expected to vest at December 31, 2025 (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementExpertiseOfManagementResponsibleTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Expertise of Management Responsible [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesFConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series F Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesFConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series F Convertible Preferred Stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right, Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of base warrant shares at issuance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Treasury Stock, Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related and Nonrelated Parties [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Biocept Asset Acquisitions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationOtherAdjustments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Other Adjustments, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationOtherAdjustments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Repurchased During Period, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of stock repurchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accelerated purchase price per share threshold percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accelerated Purchase Price Per share Threshold Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AcceleratedPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Accelerated purchase price per share threshold percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Summary of significant accounting policies.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Summary Of Significant Accounting Policies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary Of Significant Accounting Policies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditFacilityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Facility [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClinicalDevelopmentAndLicensingExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Clinical Development and Licensing Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClinicalDevelopmentAndLicensingExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Clinical Development and Licensing Expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClinicalDevelopmentAndLicensingExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Clinical, Development and Licensing Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Underwritten Public Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwritten Public Offering.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Other Adjustments, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property and equipment, gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Property, Plant and Equipment, Gross, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Property, Plant and Equipment, Gross, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregated Intrinsic Value [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Based Compensation Arrangement by Share Based Payment Award Options Aggregate Intrinsic Value [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Share based compensation arrangement by share based payment award options aggregate intrinsic value.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CounterpartyNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss before provision for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre-tax book income - worldwide:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Summary of significant accounting policies.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Summary Of Significant Accounting Policies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SummaryOfSignificantAccountingPoliciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary Of Significant Accounting Policies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested and expected to vest at December 31, 2025 (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLeaseNotYetCommencedDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, lease not yet commenced, description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLeaseNotYetCommencedDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Lease Not yet Commenced, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CumulativeChangeInOwnership_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to cumulative change in ownership in percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CumulativeChangeInOwnership_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Change In Ownership</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CumulativeChangeInOwnership_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative change in ownership</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NanoTxLicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Nano Tx license agreement Member</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NanoTxLicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nano Tx Licenses Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NanoTxLicensesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nano Tx Licenses Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Notes Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Convertible notes term.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Notes Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Foreign tax effects, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders' Equity Note [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage issuance of common stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Issuance Of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage issuance of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Goodwill and Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Paid, Excluding Capitalized Interest, Operating Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right, Exercise Price of Warrants or Rights</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant exercise price (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Public offering price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total current assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExtinguishmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Extinguishment of Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExtinguishmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Extinguishment of Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExtinguishmentOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Extinguishment of Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIncomeAndExpensesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Income and Expenses [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIncomeAndExpensesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other income (expense):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected volatility</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdjustmentsToAdditionalPaidInCapitalModificationOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustments To Additional Paid In Capital Modification Of Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdjustmentsToAdditionalPaidInCapitalModificationOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Adjustments to additional paid in capital, modification of warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdjustmentsToAdditionalPaidInCapitalModificationOfWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Modification of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_IcfrAuditorAttestationFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">ICFR Auditor Attestation Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_IcfrAuditorAttestationFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ICFR Auditor Attestation Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossAndResearchAndDevelopmentTaxCreditCarryForwardsToOffsetFutureTaxableIncomePeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Refers to the period of net operating loss and R&amp;D tax credit carry forwards to offset future taxable income.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossAndResearchAndDevelopmentTaxCreditCarryForwardsToOffsetFutureTaxableIncomePeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Operating Loss And Research And Development Tax Credit Carry Forwards To Offset Future Taxable Income Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossAndResearchAndDevelopmentTaxCreditCarryForwardsToOffsetFutureTaxableIncomePeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Period of net operating loss and R&amp;D tax credit carry forwards to offset future taxable income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResearchAndDevelopmentAwardInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development award in period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResearchAndDevelopmentAwardInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research And Development Award In Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResearchAndDevelopmentAwardInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Research and development award in period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at December 31, 2025 (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmendmentAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmendmentAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amendment agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCreditFacilityCommitmentFeePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Line of Credit Facility, Commitment Fee Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCreditFacilityCommitmentFeePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Applicable fees</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNonDilutiveMonetaryAwardsRequiredToPay_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of non-dilutive monetary awards required to pay.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNonDilutiveMonetaryAwardsRequiredToPay_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Non-dilutive Monetary awards Required to Pay</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfNonDilutiveMonetaryAwardsRequiredToPay_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of non-dilutive monetary awards required to pay</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series C convertible preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series C Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesCConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series C Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FirstPaymentReceived_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">First payment received</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FirstPaymentReceived_lbl" xlink:role="http://www.xbrl.org/2003/role/label">First Payment Received</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FirstPaymentReceived_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">First Payment Received</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock Units (RSUs) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Stock Unit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Security, Excluded EPS Calculation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Contractual obligation to provide funding of research and development costs over periods that initially exceed one year or the normal operating cycle, if longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pre Clinical Research Study Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreClinicalResearchStudyObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre-clinical Research Study Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net deferred tax assets (liability)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CompensationAndEmployeeBenefitPlansTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Compensation and Employee Benefit Plans [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CompensationAndEmployeeBenefitPlansTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Benefit Plan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InProcessResearchAndDevelopmentPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">In Process Research and Development, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InProcessResearchAndDevelopmentPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Acquired In-Process Research and Development (IPR&amp;D)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesAvailableForResale_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares available for resale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesAvailableForResale_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Shares Available For Resale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesAvailableForResale_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of shares available for resale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementStrategyAndGovernanceLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management, Strategy, and Governance [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightWarrantsExerciseRatio_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants exercise ratio</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightWarrantsExerciseRatio_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class Of Warrant Or Right Warrants Exercise Ratio</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClassOfWarrantOrRightWarrantsExerciseRatio_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Class Of Warrant Or Right Warrants Exercise Ratio.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumStockholdersEquityRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum Stockholders Equity Requirement Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumStockholdersEquityRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Minimum stockholder's equity requirement date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumStockholdersEquityRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum stockholder's equity requirement date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instruments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalSubscriptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Subscription [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalSubscriptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional Subscription.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Foreign tax effects, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B convertible preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series B Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series B Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Variable Rate [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableRateAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Indefinite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Expense and Other Assets, Current [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Current Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Finite-Lived Intangible Assets, Gross, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Carrying Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentImpairment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Impairment [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentImpairment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Weighted Average Number of Shares Outstanding, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average shares of common stock - diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Weighted average number of shares of common stock outstanding - diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_JanuaryTwoThousandAndTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">January two thousand and twenty two distribution agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_JanuaryTwoThousandAndTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">January Two Thousand and Twenty Two Distribution Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_JanuaryTwoThousandAndTwentyTwoDistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">January 2022 Distribution Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CoverAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cover</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CoverAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstruments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in fair value of derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstruments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Change In Fair Value Of Derivative Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstruments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Change in fair value of derivative instruments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstruments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in fair value of derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfAggregateAmountOfProceedsAwardedUnderCpritGrant_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of aggregate amount of proceeds awarded under CPRIT grant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfAggregateAmountOfProceedsAwardedUnderCpritGrant_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage Of Aggregate Amount Of Proceeds Awarded Under CPRIT Grant</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfAggregateAmountOfProceedsAwardedUnderCpritGrant_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of aggregate amount of proceeds awarded under CPRIT grant</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfVotesPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number Of Votes Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfVotesPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Votes Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfVotesPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of votes per share.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RemainingLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Remaining liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RemainingLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Remaining liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeOfWarrantForNotesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exchange of Warrant for Notes Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeOfWarrantForNotesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exchange of warrant for notes payable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeOfWarrantForNotesPayable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exchange of warrants for notes payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Accounts Payable and Accrued Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Accounts Payable and Accrued Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Closing bid price for common stock had fallen.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Closing Bid Price For Common Stock Had Fallen Below</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ClosingBidPriceForCommonStockHadFallenBelow_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Closing bid price for common stock had fallen below</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cancelled/forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cancelled/forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalBalanceSheetDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Balance Sheet Disclosures [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalBalanceSheetDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Composition of Certain Financial Statement Captions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioUnspecifiedDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasurySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Treasury Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasurySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury Bills [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Distribution Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Operating Segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfOperatingSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of operating segment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredRentCreditNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred rent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Information</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaintainMinimumMarketValueOfListedSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maintain Minimum Market Value of Listed Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaintainMinimumMarketValueOfListedSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maintain minimum market value of listed securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaintainMinimumMarketValueOfListedSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maintain minimum market value of listed securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">General and Administrative Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">General and administrative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total general and administrative</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TaxCreditCarryforwardExpirationDate1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit carryforward, expiration date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TaxCreditCarryforwardExpirationDate1_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Expiration date of the tax credit carryforward.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TaxCreditCarryforwardExpirationDate1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Carryforward Expiration Date1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CpritGrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">CPRIT grant funding term.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CpritGrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/label">CPRIT Grant Funding Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CpritGrantFundingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">CPRIT grant funding term, description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOther_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOther_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Intangible Asset, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rent expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted Average Remaining Contractual Life (years) [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingPercentageAfterModificationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Percentage After Modification Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingPercentageAfterModificationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing percentage after modification period.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FinancingPercentageAfterModificationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing percentage after modification period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Useful Life</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentUsefulLife_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Useful lives of the assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">New Accounting Pronouncements, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recently Issued Accounting Pronouncements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Future Minimum Annual Lease Payments under Operating Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Permanent differences</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Reconciliation Nondeductible Expense Permanent Differeces</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Income Tax Reconciliation Nondeductible Expense Permanent Differeces</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Permanent differences, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Stock option vesting period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Domestic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) from Continuing Operations before Income Taxes, Domestic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Depreciation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Depreciation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Depreciation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Depreciation, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest related to unrecognized tax benefits in interest expense and penalties</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputCommonStockMarketPriceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Common Stock Market Price [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputCommonStockMarketPriceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement Input, Common Stock Market Price.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputCommonStockMarketPriceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock Market Price [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Term of Contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lessee, operating lease, term of contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares outstanding (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Common Stock, Shares, Outstanding, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Common Stock, Shares, Outstanding, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Operating lease liabilities, current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: current portion</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Less: current portion</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction of additional paid-in-capital of reselling of securities acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reduction of Additional Paid-in-Capital of Reselling of Securities Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionOfAdditionalPaid-In-CapitalOfResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Reduction of additional paid-in-capital of reselling of securities acquired.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Convertible Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ConvertibleNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Convertible notes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation, Depletion and Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationDepletionAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Depreciation, Depletion and Amortization, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossCarryforward_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Net operating loss carryforward.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossCarryforward_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Operating Loss Carryforward</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetOperatingLossCarryforward_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net operating losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ContractualObligationFiscalYearMaturityScheduleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Contractual Obligation, Fiscal Year Maturity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ContractualObligationFiscalYearMaturityScheduleTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Future Payments under Obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementProcessesIntegratedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Processes Integrated [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Short-Term Investments, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total operating expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and development expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetImpairmentCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Impairment Charges</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetImpairmentCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Impairment charges</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetImpairmentCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Asset Impairment Charges, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetImpairmentCharges_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Impairment related to long lived assets or goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionInAdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reduction in Additional Paid in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionInAdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Reduction in additional paid in capital.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ReductionInAdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reduction of additional paid in capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesExerciseOrExchangeOfSeriesAAndBWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Exercise or Exchange of Series A and B Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesExerciseOrExchangeOfSeriesAAndBWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period, shares, exercise or exchange of series A and B warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesExerciseOrExchangeOfSeriesAAndBWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise or exchange of March 2025 Series A and B Warrants (in Shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConvertiblePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Convertible Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Twenty twenty purchase agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Twenty Twenty Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Operating Loss Carryforwards, State and Local</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State tax credit carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Cash Flows [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstrument_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Change in Fair Value of Derivative Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstrument_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Change in fair value of derivative instrument.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ChangeInFairValueOfDerivativeInstrument_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Change in fair value of derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of warrants exercised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Warrants Exercised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfWarrantsExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of warrants exercised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Issue and sale of stock, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders' equity requirement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncreaseDecreaseInDeferredGrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred grant liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncreaseDecreaseInDeferredGrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase Decrease In Deferred Grant Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncreaseDecreaseInDeferredGrantLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Increase (decrease) in deferred grant liability.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueOfWarrantLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value of Warrant Liability Reclassified to Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueOfWarrantLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair Value of Warrant Liability Reclassified to Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FairValueOfWarrantLiabilityReclassifiedToEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair value of warrant liability reclassified to equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesIssuableUponExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Shares Issuable Upon Exercise</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesIssuableUponExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of shares issuable upon exercise.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfSharesIssuableUponExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares issuable upon exercise</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmountToBeReceivedAsAwardForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amount To Be Received As Award For Research And Development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmountToBeReceivedAsAwardForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount to be received as award for research and development.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmountToBeReceivedAsAwardForResearchAndDevelopment_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amount to be received as award for research and development</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CompositionOfCertainFinancialStatementCaptionsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Composition of Certain Financial Statement Captions [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CompositionOfCertainFinancialStatementCaptionsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Composition Of Certain Financial Statement Captions [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FundingNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Funding Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FundingNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Funding notes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FundingNotesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Funding Notes [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-Based Payment Arrangement, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-Based Compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Stock-based compensation, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stockholders' Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reselling of securities acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reselling of Securities Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ResellingOfSecuritiesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Reselling of Securities Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loss per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining common stock issued and sold (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Distribution agreement member.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Distribution Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DistributionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Distribution Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxLiabilitiesOther_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Liabilities, Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxLiabilitiesOther_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementProcessesIntegratedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Processes Integrated [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrant Issuance Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Warrant issuance costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_WarrantIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Warrant issuance costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance as of December 31, 2023</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance as of December 31, 2024</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyRepurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">2020 Repurchase Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyRepurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Twenty Twenty Repurchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwentyTwentyRepurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2020 Repurchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PrivatePlacementAndPrefundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Private Placement and Prefunded Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PrivatePlacementAndPrefundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Private Placement and Prefunded Warrant[Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PrivatePlacementAndPrefundedWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Private Placement and Prefunded Warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Warrants and Rights Outstanding, Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrant liability, Remaining term (years)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Dividend Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Dividend yield</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exercise Of Pre-funded Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exercise of pre-funded warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExerciseOfPreFundedWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of pre-funded warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilityForUncertainTaxPositionsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability for Uncertainty in Income Taxes, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilityForUncertainTaxPositionsCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability for uncertain tax positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCreditFacilityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Line of Credit Facility [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating cash used for operating leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Monthly base rent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Risk-free interest rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amortization of Debt Issuance Costs and Discounts</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of deferred financing costs and debt discount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfFinancingCostsAndDiscounts_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortization of Debt Issuance Costs and Discounts, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentMeasurementInput_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Measurement Input</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentMeasurementInput_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument, Measurement Input</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPeriodIncreaseDecrease_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from investing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CompensationAndRetirementDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retirement Benefits [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accounts Payable, Current, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfMaximumCommonSharesCanBeResale_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of maximum common shares can be resale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfMaximumCommonSharesCanBeResale_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Maximum Common Shares Can Be Resale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfMaximumCommonSharesCanBeResale_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Number of maximum common shares can be resale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseNonoperating_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Nonoperating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseNonoperating_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Expense, Nonoperating, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseNonoperating_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfIncomeBeforeIncomeTaxDomesticAndForeignTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Net Loss Before Income Tax Provision</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfIncomeBeforeIncomeTaxDomesticAndForeignTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Research and Development Expense [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Research and Development [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan, Employer Matching Contribution, Percent of Match</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of matching contribution for employee contributions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred CPRIT grant revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Revenue, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Components of Deferred Tax Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComponentsOfDeferredTaxAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred tax assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfUnrecognizedTaxBenefitsExcludingAmountsPertainingToExaminedTaxReturnsRollForward_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of reconciliation of unrecognized tax benefits activity [Roll Forward]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to net operating loss expiration.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Net Operating Loss Expiration</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">NOLs expiring and adjustments to NOL</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">NOLs expiring and adjustments to NOL</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash payment information.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Payment Information [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaymentInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash payment information:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consideration to purchaser in cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock, Consideration Received on Transaction</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandTwentyFourPrefundedWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Two Thousand Twenty Four Prefunded Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandTwentyFourPrefundedWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">2024 prefunded warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_TwoThousandTwentyFourPrefundedWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2024 Pre-Funded Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Exercise of Series B Warrants from May 2024 PIPE</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock issued during period shares warrants exercise.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period Shares Warrants Exercise</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_StockIssuedDuringPeriodSharesWarrantsExercise_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock for exercise of warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Term Line of Credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Long-Term Line of Credit, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LineOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Line of credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, after Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock-based Compensation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">At the market offering program.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">At The Market Offering Program [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AtTheMarketOfferingProgramMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">At The Market Offering Program [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total unamortized compensation cost related to outstanding unvested stock options and restricted stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sale of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Restricted Stock Unit Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Revenues_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revenue recognized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Revenues_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Revenues, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Revenues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IntellectualPropertyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Intellectual Property [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IntellectualPropertyMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intellectual Property [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Investing Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash used in investing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Private Placement Share [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Private Placement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Segment Reporting Information, by Segment [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-Based Payment Arrangement, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Stock-based compensation, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PurchasePriceOfShare_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Purchase price of share.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PurchasePriceOfShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Purchase price of share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Remaining Authorized, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining authorized amount for repurchase</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cancelled/forfeited (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cancelled/forfeited</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Due after one year through five years</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Money Market [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MoneyMarketFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Money Market Funds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Related and Nonrelated Parties [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RelatedPartyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Related Party</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputRemainingTermMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Remaining Term [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputRemainingTermMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Remaining Term [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputRemainingTermMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input remaining term.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collaborative Arrangement and Arrangement Other than Collaborative [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Warrant or Right [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LegalEntityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Legal Entity [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LegalEntityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal Entity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Due after one year through five years</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Increases (decreases) in cash caused by changes in operating assets and liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and Equipment, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance as of December 31, 2025 (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance as of December 31, 2024 (in dollars per share)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InvestorFeesPursuantToSupportLetters_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investor Fees pursuant to Support Letters</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InvestorFeesPursuantToSupportLetters_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Investor fees pursuant to support letters.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_InvestorFeesPursuantToSupportLetters_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investor fees pursuant to Support Letters</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputFairValueOfCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value of Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputFairValueOfCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Fair Value Of Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputFairValueOfCommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input, fair value of common stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value, Recurring and Nonrecurring [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring and Nonrecurring [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Unrecognized Tax Benefits &#8211; Ending</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Unrecognized Tax Benefits &#8211; Beginning</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfDeductionOfInterestExpenseToEBITDA_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Deduction of Interest Expense to EBITDA</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfDeductionOfInterestExpenseToEBITDA_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of deduction of interest expense to EBITDA</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfDeductionOfInterestExpenseToEBITDA_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of deduction of interest expense to EBITDA</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwritingAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Underwriting Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwritingAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwriting Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RegularPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Regular Purchase Price Per Share Threshold Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RegularPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Regular purchase price per share threshold percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RegularPurchasePricePerShareThresholdPercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Regular purchase price per share threshold percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Frequency [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Frequency [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramAuthorizedAmount1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Repurchase Program Authorized Dollar Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramAuthorizedAmount1_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Authorized amount of repurchase of stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Change in Accounting Principle, Accounting Standards Update, Adoption Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdoptionDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in accounting principle, accounting standards update, adoption date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Intangible Asset, Finite-Lived [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Due in one year or less</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Event Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Subsequent Event Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FloorPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Floor Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FloorPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Floor price.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FloorPrice_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Floor price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Biocept Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Biocept Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Biocept Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Expected term (years)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recurring Basis [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum lease payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total minimum lease payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedLicensePayable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Accrued license payable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedLicensePayable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued License Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AccruedLicensePayable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued payments due to NanoTx</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, Undiscounted Excess Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Less: amount representing interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Research credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">R&amp;D Credits, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Components [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LinesOfCreditCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Outstanding balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LinesOfCreditCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Line of Credit, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LinesOfCreditCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Line of credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nonoperating Income (Expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonoperatingIncomeExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other income (expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Activity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock Option Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseholdImprovementsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Leasehold Improvements, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseholdImprovementsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leasehold improvements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAssetAcquisitionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Biocept Asset Acquisitions [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAssetAcquisitionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Biocept asset acquisitions.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_BioceptAssetAcquisitionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Biocept Asset Acquisitions [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentAnnualReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Annual Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentAnnualReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Annual Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Due after five years</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Prepaid Insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrepaidInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prepaid insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrossProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Gross proceeds from issuance of common stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrossProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gross Proceeds from Issuance of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_GrossProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Aggregate gross proceeds from sales of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock unit vesting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock option contractual term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">March 2025 Series A Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">March Two Thousand Twenty Five Series A Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">March Two Thousand Twenty Five Series A Warrants Member.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationTaxContingencies_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">FIN 48, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationTaxContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Tax Contingency, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationTaxContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Effective Income Tax Rate Reconciliation, Tax Contingency, Amount, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Operating Loss Carryforwards, Domestic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal tax carry forward</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DepartmentOfDefenseAwardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Department of Defense Award [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_DepartmentOfDefenseAwardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Department of defense award.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ProceedsFromIssuanceOfCommonStockNetOfOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of common stock, net of offering costs of $0.2 million</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ProceedsFromIssuanceOfCommonStockNetOfOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds From Issuance Of Common Stock Net of Offering Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ProceedsFromIssuanceOfCommonStockNetOfOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Proceeds from issuance of common stock net of offering costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Voting stock, value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, $0.001 par value; 2,000,000,000 shares authorized; 138,934,281 shares issued and 138,675,856 outstanding as of December 31, 2025, 100,000,000 shares authorized; 6,154,758 shares issued and 5,896,333 outstanding as of December 31, 2024, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Income (Loss) Available to Common Stockholders, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net loss attributable to common stockholders - diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Rule 10b51 Arr Modified Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Rule 10b51 Arr Modified Flag.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_Rule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Rule 10b51 Arr Modified Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumGrantAmountToBeReceivedAsPerGrantContract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Maximum grant amount to be received as per grant contract.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumGrantAmountToBeReceivedAsPerGrantContract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum Grant Amount to be Received as per Grant Contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MaximumGrantAmountToBeReceivedAsPerGrantContract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum grant amount to be received as per grant contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsAndSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">March Two Thousand Twenty Five Series A Warrants and Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsAndSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">March 2025 Series A and March 2025 Series B common stock warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsAndSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">March 2025 Series A and Series B Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Operating Loss Carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net operating loss carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Tax Assets, Operating Loss Carryforwards, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Deferred tax assets related to NOL carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementProcessesForAssessingIdentifyingAndManagingThreatsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State and local income taxes, net of federal income tax effect:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">State and local income taxes, net of federal income tax effect: Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LincolnParkPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lincoln Park Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LincolnParkPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Lincoln Park Purchase Agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LincolnParkPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lincoln Park Purchase Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Future Amortization Expense on Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwentyTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">May Twenty Twenty Four Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwentyTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">May twenty twenty four Series B warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MayTwentyTwentyFourSeriesBWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">May 2024 Series B Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumBidRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum Bid Requirement Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumBidRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Minimum bid requirement date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MinimumBidRequirementDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum bid requirement date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityPublicFloat_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Public Float</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityPublicFloat_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Public Float</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares authorized (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Payable, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets by Major Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDebtTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Debt [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDebtTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Face Value to Book Value Reconciliation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">February Two Thousand Twenty Five Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">February two thousand twenty five warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_FebruaryTwoThousandTwentyFiveWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">February 2025 Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCommissionOnGrossProceedsFromSaleOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of commission on gross proceeds from sale of common stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCommissionOnGrossProceedsFromSaleOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Commission on Gross Proceeds from Sale of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCommissionOnGrossProceedsFromSaleOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Percentage of commission on gross proceeds from sale of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Percent, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of cross border tax laws, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Revenue from Contract with Customer [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RevenueFromContractWithCustomerTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Term Loan Obligations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDeferredCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Deferred Costs, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDeferredCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Deferred Costs, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDeferredCostsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred costs (Note 7)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalPeriodForRegainComplianceOnAchievementOfCompliance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Period for Regain Compliance on Achievement of Compliance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalPeriodForRegainComplianceOnAchievementOfCompliance_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Additional period for regain compliance on achievement of compliance.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AdditionalPeriodForRegainComplianceOnAchievementOfCompliance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional period for regain compliance on achievement of compliance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sales of short-term investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfShortTermInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale of Short-Term Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series B Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesBWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B Warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityVoluntaryFilers_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Voluntary Filers</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityVoluntaryFilers_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Voluntary Filers</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PersonnelRelatedExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Personnel Related Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PersonnelRelatedExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Personnel Related Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PersonnelRelatedExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Personnel Related Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of treasury stock (in Shares)</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Shares, Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Additional Paid in Capital, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">In process research and development acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For I P R D Asset Acquired In An Asset Acquisition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CashPaidForIPRDAssetAcquiredInAnAssetAcquisition_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for IPRD asset acquired in an asset acquisition.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmendmentAndRestatementsMay2024PrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment and Restatements May 2024 Private Placement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_AmendmentAndRestatementsMay2024PrivatePlacementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amendment and restatements May 2024 private placement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsequentEventsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subsequent Events [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ValuationAndQualifyingAccountsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts Payable and Accrued Liabilities, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts payable and accrued expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accounts payable and accrued expenses, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="cyd_CybersecurityRiskManagementPositionsOrCommitteesResponsibleFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cybersecurity Risk Management Positions or Committees Responsible [Flag]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Three</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Expense (Benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision or benefit for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Provision for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesGrossUnrealizedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Unrealized Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesGrossUnrealizedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrealized loss on available-for-sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesGrossUnrealizedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total unrealized loss on available-for-sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Frequency [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Frequency [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireProductiveAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Productive Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireProductiveAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments to Acquire Productive Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireProductiveAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total cash payment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross proceeds from sale of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from sale of common stock, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from sale of common stock under Lincoln Park Purchase Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SubscriptionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Subscription Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SubscriptionAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Subscription Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share Based Compensation Arrangement By Share Based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Key Level 3 Inputs Used in Valuation of Warrants Liability at Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Unpaid Offering Costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unpaid Offering Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnpaidOfferingCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unpaid offering cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConcentrationRiskCreditRisk_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Concentration Risk</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConcentrationRiskCreditRisk_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Concentration Risk, Credit Risk, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputInterestRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Interest Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputInterestRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Measurement input interest rate.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_MeasurementInputInterestRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Property, Plant, and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments to Acquire Property, Plant, and Equipment, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of property and equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LeaseAnnualIncreaseRateOfBaseRent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease annual increase rate of base rent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LeaseAnnualIncreaseRateOfBaseRent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease annual Increase Rate of Base Rent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_LeaseAnnualIncreaseRateOfBaseRent_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Lease annual increase rate of base rent.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercisable at December 31, 2025</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value of Financial Instruments, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Gross decreases &#8211; tax positions in prior period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-Based Compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SecuritiesPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Securities Purchase Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SecuritiesPurchaseAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Securities purchase agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Income taxes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_IncomeTaxesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Taxes [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PaymentToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment to investors pursuant to Letter Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PaymentToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Payment to investors pursuant to letter agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PaymentToInvestorsPursuantToLetterAgreement_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Payment to investors pursuant to Letter Agreement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LegalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Legal Fees</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LegalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Legal fees</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock, Number of Shares Issued in Transaction</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series A Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series A Warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Issue and sale of share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Issue and sale of share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance of common stock (in shares)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease expense:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vested</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Vested</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net loss per share, diluted</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Segment Reporting Information, by Segment [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SalesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Sales agreement.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SalesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sales Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SalesAgreementMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Sales Agreement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RedemptionOfNotesByIssuanceOfCommonStockPrefundedWarrantsAndWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Redemption of notes by issuance of common stock, prefunded warrants and warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RedemptionOfNotesByIssuanceOfCommonStockPrefundedWarrantsAndWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Redemption of notes by issuance of common stock, pre-funded warrants and warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Auditor Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Auditor Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Cash and Cash Equivalent, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Restricted Cash and Cash Equivalent, Current, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentFeeAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Fee Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentFeeAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fees amount associated with loan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLinesOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Lines of Credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLinesOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds from Lines of Credit, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLinesOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from credit facility</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Examination, Penalties and Interest Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest or penalties related to income tax matters</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income Tax Examination, Penalties and Interest Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument, Face Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Original loan amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Aggregate principal amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonCashFinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non-Cash Financing Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonCashFinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-cash financing expense.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonCashFinancingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noncash financing expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Tax Credit Carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax credit carryforwards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Tax Assets, Tax Credit Carryforwards, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Counterparty Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationTaxCreditsResearch_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">R&amp;D Credits, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxReconciliationTaxCreditsResearch_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfCashlessWarrantsExcercisedForCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Cashless Warrants Excercised for Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfCashlessWarrantsExcercisedForCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of cashless warrants excercised for common stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfCashlessWarrantsExcercisedForCommonStock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cashless warrants excercised for common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LitigationCaseAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Case [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_LitigationCaseAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Litigation Case</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Weighted Average Remaining Lease Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease, weighted average remaining term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total lease expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComputerSoftwareIntangibleAssetMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Software [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComputerSoftwareIntangibleAssetMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Computer Software, Intangible Asset [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number Of Preferred Stock Shares Exercised.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number Of Preferred Stock Shares Exercised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NumberOfPreferredStockSharesExercised_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of preferred stock, shares converted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Property and equipment, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property and equipment, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash, cash equivalents, and restricted cash at end of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash, cash equivalents, and restricted cash at beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total cash, cash equivalents, and restricted cash presented in the consolidated statements of cash flows</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Income (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Operating loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCreditFacilityCannotExceedCollateralizedMarketableSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of credit facility cannot exceed collateralized marketable securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCreditFacilityCannotExceedCollateralizedMarketableSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Percentage of Credit Facility Cannot Exceed Collateralized Marketable Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PercentageOfCreditFacilityCannotExceedCollateralizedMarketableSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Percentage of credit facility cannot exceed collateralized marketable securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Effective income tax rate reconciliation warrants.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrants_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrants_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Warrants, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Deficit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and Cash Equivalents [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Noncash Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-Based Payment Arrangement, Noncash Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Stock compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Price Volatility [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Volatility [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Payment of offering costs related to sale of common stock</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Issuance costs paid in common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Offering costs for sale of common stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RestrictedBeneficialOwnershipLevelResultOfExerciseOfWarrantToReceivePreFundedWarrant_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted beneficial ownership level result of exercise of warrant to receive pre-funded warrant</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RestrictedBeneficialOwnershipLevelResultOfExerciseOfWarrantToReceivePreFundedWarrant_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Beneficial Ownership Level Result of Exercise of Warrant To Receive Pre-funded Warrant</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_RestrictedBeneficialOwnershipLevelResultOfExerciseOfWarrantToReceivePreFundedWarrant_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Restricted beneficial ownership level result of exercise of warrant to receive pre-funded warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Rule 10b51 Arr Modified Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non rule 10b51 arr modified flag.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NonRule10B51ArrModifiedFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non Rule 10b51 Arr Modified Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Authorized, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of shares agreed to return</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ManufacturingAgreementWithSpectronRXMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Manufacturing Agreement with SpectronRX [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NoLongerRequiredPercentageOfProceedsToRepayPurchasersFromCapitalRaised_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">No longer required percentage of proceeds to repay purchasers from capital raised.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NoLongerRequiredPercentageOfProceedsToRepayPurchasersFromCapitalRaised_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">No longer required percentage of proceeds to repay purchasers from capital raised</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwriterMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwriter.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwriterMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Underwriter [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_UnderwriterMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Underwriter [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Weighted Average Discount Rate, Percent</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfficeAndComputerEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">The gross amount of office and computer equipment cost as of the balance sheet date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_OfficeAndComputerEquipmentGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Office And Computer Equipment Gross</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Grants Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantsReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant revenue receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ChangeInAccountingPrincipleAccountingStandardsUpdateAdopted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Change in accounting principle, accounting standards update, adopted</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorLocation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Auditor Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AuditorLocation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Auditor Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Due after five years</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Investments, Fair Value Disclosure, Total</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Other Current Assets [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherCurrentAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Current Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockholdersEquityNoteWarrantsOrRightsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockholdersEquityNoteWarrantsOrRightsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Warrants Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Grant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Grant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Government Corporations and Agencies Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Government Agency Bonds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Antidilutive Securities Excluded from Diluted (Loss) per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxAuthorityDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Tax Jurisdiction [Domain]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrantsAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Effective Income Tax Rate Reconciliation Warrants Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrantsAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Effective income tax rate reconciliation warrants amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrantsAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Warrants, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_EffectiveIncomeTaxRateReconciliationWarrantsAmount_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Warrants, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreFundedWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pre-Funded Warrants [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_PreFundedWarrantsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Pre-funded warrants member.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetProceedsAfterDeductingTheUnderwritingDiscountsAndCommissionsAndOtherEstimatedOfferingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Proceeds After Deducting the Underwriting Discounts and Commissions and Other Estimated Offering Expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetProceedsAfterDeductingTheUnderwritingDiscountsAndCommissionsAndOtherEstimatedOfferingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Net proceeds after deducting the underwriting discounts and commissions and other estimated offering expenses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetProceedsAfterDeductingTheUnderwritingDiscountsAndCommissionsAndOtherEstimatedOfferingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net proceeds after deducting the underwriting discounts and commissions and other estimated offering expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_NetProceedsAfterDeductingTheUnderwritingDiscountsAndCommissionsAndOtherEstimatedOfferingExpenses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net proceeds from the offering after deducting the underwriting discounts and commissions and other estimated offering expenses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetAcquisitionLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Acquisition [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLinesOfCredit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Repayment of credit facility</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLinesOfCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Repayments of Lines of Credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accretion of discount on short-term investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accretion (Amortization) of Discounts and Premiums, Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accretion of discount on short-term investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingExpenseInformationUsedByCodmTypeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, Expense Information Used by CODM, Type [Extensible Enumeration]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Exchange [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_ExchangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Exchange.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RecordedUnconditionalPurchaseObligationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Recorded Unconditional Purchase Obligation [Line Items]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityTaxIdentificationNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Tax Identification Number</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAWarrantAndSeriesBWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series A Warrant and Series B Warrant [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_SeriesAWarrantAndSeriesBWarrantMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series a warrant and series b warrant.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasisAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SharePrice_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Price</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_LocalPhoneNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Local Phone Number</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="pstv_CancerPreventionAndResearchInstituteOfTexasContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cancer prevention and research institute of texas contract.</link:label>
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  <xsd:element id="pstv_MarchTwoThousandTwentyFiveSeriesBWarrantsMember" name="MarchTwoThousandTwentyFiveSeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_UnpaidOfferingCosts" name="UnpaidOfferingCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_LincolnParkPurchaseAgreementMember" name="LincolnParkPurchaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_InitialCommitmentFee" name="InitialCommitmentFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_NetOperatingLossCarryforward" name="NetOperatingLossCarryforward" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_LetterAgreementMember" name="LetterAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_NetOperatingLossAndResearchAndDevelopmentTaxCreditCarryForwardsToOffsetFutureTaxableIncomePeriod" name="NetOperatingLossAndResearchAndDevelopmentTaxCreditCarryForwardsToOffsetFutureTaxableIncomePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageOfProceedsToRepayPurchasersFromCapitalRaised" name="PercentageOfProceedsToRepayPurchasersFromCapitalRaised" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageIssuanceOfCommonStock" name="PercentageIssuanceOfCommonStock" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_CharlottesvilleMember" name="CharlottesvilleMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_WarrantIssuanceExpenses" name="WarrantIssuanceExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MayTwoThousandTwentyFourPurchaseAgreementMember" name="MayTwoThousandTwentyFourPurchaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_May2024PrivatePlacementMember" name="May2024PrivatePlacementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_IncomeTaxesTable" name="IncomeTaxesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AmendmentAgreementMember" name="AmendmentAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_CumulativeChangeInOwnership" name="CumulativeChangeInOwnership" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodValueExerciseOrExchangeOfSeriesAAndBWarrants" name="StockIssuedDuringPeriodValueExerciseOrExchangeOfSeriesAAndBWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_EffectiveIncomeTaxRateReconciliationWarrants" name="EffectiveIncomeTaxRateReconciliationWarrants" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ProceedsFromSaleOfCommonStockPrefundedWarrantsAndWarrants" name="ProceedsFromSaleOfCommonStockPrefundedWarrantsAndWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_AtTheMarketOfferingProgramMember" name="AtTheMarketOfferingProgramMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ClassOfWarrantOrRightExpirationPeriod" name="ClassOfWarrantOrRightExpirationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_DepartmentOfDefenseAwardMember" name="DepartmentOfDefenseAwardMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ExerciseOfPreFundedWarrantsShares" name="ExerciseOfPreFundedWarrantsShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_OperatingLossCarryforwardsExpirationDates1" name="OperatingLossCarryforwardsExpirationDates1" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_StockBasedCompensation2015EquityIncentivePlan1Member" name="StockBasedCompensation2015EquityIncentivePlan1Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_TwentyTwentyPurchaseAgreementMember" name="TwentyTwentyPurchaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_WarrantLiabilityMember" name="WarrantLiabilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_DeferredTaxAssetsValuationAllowances" name="DeferredTaxAssetsValuationAllowances" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityModificationAndExtinguishment" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityModificationAndExtinguishment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_IncreaseDecreaseInDeferredGrantLiability" name="IncreaseDecreaseInDeferredGrantLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_PercentageOfDeductionOfInterestExpenseToEBITDA" name="PercentageOfDeductionOfInterestExpenseToEBITDA" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_NumberOfMaximumCommonSharesCanBeResale" name="NumberOfMaximumCommonSharesCanBeResale" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ContractTerminationDate" name="ContractTerminationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_UnpaidLiabilityToInvestorsPursuantToLetterAgreement" name="UnpaidLiabilityToInvestorsPursuantToLetterAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_TwentyTwentyRepurchaseAgreementMember" name="TwentyTwentyRepurchaseAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_CanaccordGenuityLLCMember" name="CanaccordGenuityLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MinimumBidRequirementDate" name="MinimumBidRequirementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ClosingStockPriceNotBelowZeroPointOneZeroMember" name="ClosingStockPriceNotBelowZeroPointOneZeroMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ExerciseOfPreFundedWarrants" name="ExerciseOfPreFundedWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_FebruaryTwoThousandTwentyFiveSecuritiesPurchaseAndExchangeAgreementsMember" name="FebruaryTwoThousandTwentyFiveSecuritiesPurchaseAndExchangeAgreementsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AccruedLicensePayable" name="AccruedLicensePayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_SummaryOfSignificantAccountingPoliciesTable" name="SummaryOfSignificantAccountingPoliciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_RemainingLiability" name="RemainingLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_TaxCreditCarryforwardExpirationDate1" name="TaxCreditCarryforwardExpirationDate1" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_MeasurementInputRemainingTermMember" name="MeasurementInputRemainingTermMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MayTwentyTwentyFourSeriesBWarrantsMember" name="MayTwentyTwentyFourSeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_WarrantsPolicyPolicyTextBlock" name="WarrantsPolicyPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageOfGrantProceedsWithInterestNotExceedAnnually" name="PercentageOfGrantProceedsWithInterestNotExceedAnnually" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_InvestorLiabilityPursuantToLetterAgreement" name="InvestorLiabilityPursuantToLetterAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_RightsRelatedToDistributionOfAssets" name="RightsRelatedToDistributionOfAssets" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_LGOnePropertyOwnerLPMember" name="LGOnePropertyOwnerLPMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_JanuaryTwoThousandAndTwentyTwoDistributionAgreementMember" name="JanuaryTwoThousandAndTwentyTwoDistributionAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AdditionalPeriodForRegainComplianceOnAchievementOfCompliance" name="AdditionalPeriodForRegainComplianceOnAchievementOfCompliance" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ResearchAndDevelopmentAwardInPeriod" name="ResearchAndDevelopmentAwardInPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_SeriesAConvertiblePreferredStockMember" name="SeriesAConvertiblePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_IssuanceOfCommonStockPrefundedWarrantsAndWarrantsForDebtRepayment" name="IssuanceOfCommonStockPrefundedWarrantsAndWarrantsForDebtRepayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_RegularPurchasePricePerShareThresholdPercentage" name="RegularPurchasePricePerShareThresholdPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageOfAggregateAmountOfProceedsAwardedUnderCpritGrant" name="PercentageOfAggregateAmountOfProceedsAwardedUnderCpritGrant" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_LicenseAgreementDisclosureTextBlock" name="LicenseAgreementDisclosureTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_FirstPaymentReceived" name="FirstPaymentReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_CashPaidDuringPeriodForAbstract" name="CashPaidDuringPeriodForAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ClassOfWarrantOrRightWarrantsExerciseRatio" name="ClassOfWarrantOrRightWarrantsExerciseRatio" type="xbrli:pureItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_FinancingExpense" name="FinancingExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_FloorPrice" name="FloorPrice" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_NumberOfPreferredStockSharesExercised" name="NumberOfPreferredStockSharesExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_CompositionOfCertainFinancialStatementCaptionsAbstract" name="CompositionOfCertainFinancialStatementCaptionsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MayTwoThousandTwentyFourSeriesBWarrantsMember" name="MayTwoThousandTwentyFourSeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount" name="IncomeTaxReconciliationNondeductibleExpensePermanentDifferencesAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_SeriesBWarrantMember" name="SeriesBWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_NonCashFinancingExpense" name="NonCashFinancingExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_PaymentToInvestorsPursuantToLetterAgreement" name="PaymentToInvestorsPursuantToLetterAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_CashPaymentInformationAbstract" name="CashPaymentInformationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PercentageOfDeductionOfBonusDepreciationOnEligiblePropertyAcquired" name="PercentageOfDeductionOfBonusDepreciationOnEligiblePropertyAcquired" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ScheduleOfOperatingAndFinancingLeaseLiabilityMaturityTableTextBlock" name="ScheduleOfOperatingAndFinancingLeaseLiabilityMaturityTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_EffectiveIncomeTaxRateReconciliationWarrantsAmount" name="EffectiveIncomeTaxRateReconciliationWarrantsAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_NoLongerRequiredPercentageOfProceedsToRepayPurchasersFromCapitalRaised" name="NoLongerRequiredPercentageOfProceedsToRepayPurchasersFromCapitalRaised" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_SummaryOfSignificantAccountingPoliciesLineItems" name="SummaryOfSignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_NumberOfVotesPerShare" name="NumberOfVotesPerShare" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PrefundedWarrantMember" name="PrefundedWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MaximumGrantAmountToBeReceivedAsPerGrantContract" name="MaximumGrantAmountToBeReceivedAsPerGrantContract" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_PersonnelRelatedExpensesMember" name="PersonnelRelatedExpensesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_TwoThousandTwentyFourPrefundedWarrantsMember" name="TwoThousandTwentyFourPrefundedWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PercentageOfNetOperatingLossCarryforwardsAvailableForOffsettingAgainstFutureTaxableIncome" name="PercentageOfNetOperatingLossCarryforwardsAvailableForOffsettingAgainstFutureTaxableIncome" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_OptionsMember" name="OptionsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ExchangeOfWarrantForNotesPayable" name="ExchangeOfWarrantForNotesPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_SeriesAWarrantMember" name="SeriesAWarrantMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ChangeInFairValueOfDerivativeInstrument" name="ChangeInFairValueOfDerivativeInstrument" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_ClosingStockPriceNotBelowZeroPointFiveZeroMember" name="ClosingStockPriceNotBelowZeroPointFiveZeroMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_InitialSubscriptionMember" name="InitialSubscriptionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_BioceptAssetAcquisitionsMember" name="BioceptAssetAcquisitionsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_UnderwritingAgreementMember" name="UnderwritingAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AmountToBeReceivedAsAwardForResearchAndDevelopment" name="AmountToBeReceivedAsAwardForResearchAndDevelopment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_ExchangeOfWarrantsForNotesPayable" name="ExchangeOfWarrantsForNotesPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_ResellingOfSecuritiesAcquired" name="ResellingOfSecuritiesAcquired" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_CommonStockIssuedForResearchAndDevelopment" name="CommonStockIssuedForResearchAndDevelopment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_MaximumBeneficialOwnershipPercentageByElectionOfHolder" name="MaximumBeneficialOwnershipPercentageByElectionOfHolder" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsMember" name="MarchTwoThousandTwentyFiveSeriesAWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_LicenseAgreementAbstract" name="LicenseAgreementAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ExtinguishmentOfWarrants" name="ExtinguishmentOfWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_AccruedResearchAndDevelopmentStudies" name="AccruedResearchAndDevelopmentStudies" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_IncreaseDecreaseInGrantReceivable" name="IncreaseDecreaseInGrantReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_CommonStockSalesAvailableForIssuance" name="CommonStockSalesAvailableForIssuance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_CancerPreventionAndResearchInstituteOfTexasContractMember" name="CancerPreventionAndResearchInstituteOfTexasContractMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_OfficeAndComputerEquipmentGross" name="OfficeAndComputerEquipmentGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_ConsiderationPaidToPreferredStockHolders" name="ConsiderationPaidToPreferredStockHolders" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_SeriesFConvertiblePreferredStockMember" name="SeriesFConvertiblePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ReductionInAdditionalPaidInCapital" name="ReductionInAdditionalPaidInCapital" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_NumberOfSharesAvailableForResale" name="NumberOfSharesAvailableForResale" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ScheduleOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" name="ScheduleOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageOfCommissionOnGrossProceedsFromSaleOfCommonStock" name="PercentageOfCommissionOnGrossProceedsFromSaleOfCommonStock" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_FebruaryTwoThousandTwentyFiveWarrantsMember" name="FebruaryTwoThousandTwentyFiveWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PeriodForRegainCompliance" name="PeriodForRegainCompliance" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_CpritGrantFundingTerm" name="CpritGrantFundingTerm" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_LeaseAnnualIncreaseRateOfBaseRent" name="LeaseAnnualIncreaseRateOfBaseRent" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_InvestorFeesPursuantToSupportLetters" name="InvestorFeesPursuantToSupportLetters" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_SeptemberTwoThousandAndTwentyTwoDistributionAgreementMember" name="SeptemberTwoThousandAndTwentyTwoDistributionAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PercentageOfNonDilutiveMonetaryAwardsRequiredToPay" name="PercentageOfNonDilutiveMonetaryAwardsRequiredToPay" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_RedemptionOfNotesByIssuanceOfCommonStockPrefundedWarrantsAndWarrants" name="RedemptionOfNotesByIssuanceOfCommonStockPrefundedWarrantsAndWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_NanoTxLicensesAgreementMember" name="NanoTxLicensesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodSharesWarrantsExerciseShares" name="StockIssuedDuringPeriodSharesWarrantsExerciseShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_MayTwoThousandTwentyFourSeriesAWarrantsMember" name="MayTwoThousandTwentyFourSeriesAWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodSharesExerciseOrExchangeOfSeriesAAndBWarrants" name="StockIssuedDuringPeriodSharesExerciseOrExchangeOfSeriesAAndBWarrants" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_AdditionalAcceleratedPurchasePricePerShareThresholdPercentage" name="AdditionalAcceleratedPurchasePricePerShareThresholdPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_TwoThousandEighteenRightsOfferingMember" name="TwoThousandEighteenRightsOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_IncomeTaxesLineItems" name="IncomeTaxesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities" name="CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_SupportLetterParticipationRightsPeriod" name="SupportLetterParticipationRightsPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_SalesAgreementMember" name="SalesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ProfessionalExpensesMember" name="ProfessionalExpensesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_CongressionallyDirectedMedicalResearchProgramsMember" name="CongressionallyDirectedMedicalResearchProgramsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodValueReclassificationOfWarrantsToEquity" name="StockIssuedDuringPeriodValueReclassificationOfWarrantsToEquity" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_DebtInstrumentFloorRate" name="DebtInstrumentFloorRate" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_SubscriptionAgreementMember" name="SubscriptionAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_RestrictedBeneficialOwnershipLevelResultOfExerciseOfWarrantToReceivePreFundedWarrant" name="RestrictedBeneficialOwnershipLevelResultOfExerciseOfWarrantToReceivePreFundedWarrant" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ModificationPeriod" name="ModificationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_AdditionalSubscriptionMember" name="AdditionalSubscriptionMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_Other" name="Other" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_SeriesBWarrantsMember" name="SeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MarchTwoThousandTwentyFiveSeriesAAndBWarrantsMember" name="MarchTwoThousandTwentyFiveSeriesAAndBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_WarrantIssuanceCosts" name="WarrantIssuanceCosts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_NonRule10B51ArrModifiedFlag" name="NonRule10B51ArrModifiedFlag" type="xbrli:booleanItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PotentialFinancingPercentage" name="PotentialFinancingPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_MeasurementInputFairValueOfCommonStockMember" name="MeasurementInputFairValueOfCommonStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ExchangeMember" name="ExchangeMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_SharesIssuedSharesShareBasedPaymentArrangementForfeited" name="SharesIssuedSharesShareBasedPaymentArrangementForfeited" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ConvertibleNotesTerm" name="ConvertibleNotesTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ProceedsFromIssuanceOfNotesPayableAndWarrants" name="ProceedsFromIssuanceOfNotesPayableAndWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_InitialCommitmentShares" name="InitialCommitmentShares" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="pstv_SeriesCConvertiblePreferredStockMember" name="SeriesCConvertiblePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration" name="EffectiveIncomeTaxRateReconciliationNetOperatingLossExpiration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PreferredStockDividendRatePercentageEliminatedDate" name="PreferredStockDividendRatePercentageEliminatedDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_MarchTwoThousandTwentyFiveSeriesAWarrantsAndSeriesBWarrantsMember" name="MarchTwoThousandTwentyFiveSeriesAWarrantsAndSeriesBWarrantsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AdjustmentsToAdditionalPaidInCapitalModificationOfWarrants" name="AdjustmentsToAdditionalPaidInCapitalModificationOfWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_ManufacturingAgreementWithSpectronRXMember" name="ManufacturingAgreementWithSpectronRXMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces" name="IncomeTaxReconciliationNondeductibleExpensePermanentDiffereces" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_AggregatePurchasePrice" name="AggregatePurchasePrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_PreClinicalResearchStudyObligationsMember" name="PreClinicalResearchStudyObligationsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PotentialCashPayment" name="PotentialCashPayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_IssuanceOfCommonStockSharesPrefundedWarrantsAndWarrantsForDebtRepayment" name="IssuanceOfCommonStockSharesPrefundedWarrantsAndWarrantsForDebtRepayment" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_PercentageOfCreditFacilityCannotExceedCollateralizedMarketableSecurities" name="PercentageOfCreditFacilityCannotExceedCollateralizedMarketableSecurities" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_LiabilityToInvestorsPursuantToLetterAgreement" name="LiabilityToInvestorsPursuantToLetterAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="pstv_MinimumStockholdersEquityRequirementDate" name="MinimumStockholdersEquityRequirementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_LincolnParkCapitalFundLLCMember" name="LincolnParkCapitalFundLLCMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PercentageAgreedToRepayPurchasersHoldingSecurities" name="PercentageAgreedToRepayPurchasersHoldingSecurities" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_GrantFundingTerm" name="GrantFundingTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_ClinicalDevelopmentAndLicensingExpensesMember" name="ClinicalDevelopmentAndLicensingExpensesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_AmendmentAndRestatementsMay2024PrivatePlacementMember" name="AmendmentAndRestatementsMay2024PrivatePlacementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_PershingCreditFacilityMember" name="PershingCreditFacilityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_StockBasedCompensation2020EquityIncentivePlanMember" name="StockBasedCompensation2020EquityIncentivePlanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_TermLoanMember" name="TermLoanMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_FundingNotesMember" name="FundingNotesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_MaintainMinimumMarketValueOfListedSecurities" name="MaintainMinimumMarketValueOfListedSecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodSharesRestrictedStockUnitVesting" name="StockIssuedDuringPeriodSharesRestrictedStockUnitVesting" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_AcceleratedPurchasePricePerShareThresholdPercentage" name="AcceleratedPurchasePricePerShareThresholdPercentage" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_FacilityAndOtherOverheadExpensesMember" name="FacilityAndOtherOverheadExpensesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="pstv_ClosingBidPriceForCommonStockHadFallenBelow" name="ClosingBidPriceForCommonStockHadFallenBelow" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="pstv_StockIssuedDuringPeriodSharesWarrantsExercise" name="StockIssuedDuringPeriodSharesWarrantsExercise" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_AggregateExpenseIncludingFeeAndDisbursementExpenses" name="AggregateExpenseIncludingFeeAndDisbursementExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="pstv_BioceptAgreementMember" name="BioceptAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
</xsd:schema>
