1. Nature of Business, Basis of Presentation and Segment Information

Nature of Business

Karyopharm Therapeutics Inc., a Delaware corporation (collectively with its subsidiaries, the “Company,” “we,” “us,” or “our”), is a commercial-stage pharmaceutical company pioneering novel cancer therapies and dedicated to the discovery, development and commercialization of first-in-class drugs directed against nuclear export for the treatment of cancer. We were incorporated in Delaware on December 22, 2008 and have a principal place of business in Newton, Massachusetts.

Our scientific expertise is based upon an understanding of the regulation of intracellular communication between the nucleus and the cytoplasm. We have discovered and are developing and commercializing novel, small molecule Selective Inhibitor of Nuclear Export compounds that inhibit the nuclear export protein exportin 1. Our primary focus is on marketing XPOVIO®(selinexor) in its currently approved indications, as well as developing and seeking the regulatory approval of selinexor as an oral agent targeting multiple high unmet cancer indications, including our lead clinical programs in myelofibrosis and our other late-stage clinical programs in endometrial cancer and multiple myeloma.

Our lead asset, XPOVIO, received its initial U.S. approval from the U.S. Food and Drug Administration in July 2019 and is currently approved and marketed for the following indications: (i) in combination with bortezomib and dexamethasone for the treatment of adult patients with multiple myeloma who have received at least one prior therapy; (ii) in combination with dexamethasone for the treatment of adult patients with relapsed or refractory multiple myeloma who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody; and (iii) for the treatment of adult patients with relapsed or refractory diffuse large B-cell lymphoma (“DLBCL”), not otherwise specified, including DLBCL arising from follicular lymphoma, after at least two lines of systemic therapy. The commercialization of XPOVIO and NEXPOVIO® (selinexor) (the brand name for selinexor in Europe and the United Kingdom) outside of the U.S. is managed by our partners in their respective territories. XPOVIO/NEXPOVIO has received regulatory approval in various indications in 50 countries outside of the U.S. and is commercially available in a growing number of countries as our partners continue to secure reimbursement approvals.

Liquidity, Capital Resources and Going Concern

We have historically financed our operations primarily through a combination of proceeds from (i) product revenue sales, (ii) public and private placements of equity securities, (iii) the issuance of convertible debt, (iv) a term loan, (v) our deferred royalty obligation, (vi) at the market offerings and (vii) business development activities. As of June 30, 2025, we had $51.7 million of cash, cash equivalents and investments and an accumulated deficit of $1.6 billion. We have incurred significant operating losses since our inception and we anticipate that we will continue to incur significant operating losses to maintain our research and development programs, including as we continue to develop and seek regulatory approval of selinexor for multiple cancer indications, and to support our continued operations. As a result, our continued operations are dependent on our ability to raise additional funding or enter in other strategic alternatives and marketing XPOVIO in its currently approved indications. Based on our current business plan and current capital resources, given the uncertainty regarding the availability of additional funding or other strategic alternatives and considering our debt service obligations, including our 3.00% convertible senior notes maturing on October 15, 2025 (the “2025 Notes”) with an aggregate principal amount of $24.5 million and a requirement of our Credit Agreement, as defined below, and the indenture governing our 6.00% convertible senior notes due 2029 (the “2029 Notes”) to maintain cash, cash equivalents and investments of at least $25.0 million at all times, we have concluded that there is substantial doubt regarding our ability to continue as a going concern within one year after the date the accompanying condensed consolidated financial statements are issued. We plan to address the conditions that raise substantial doubt regarding our ability to continue as a going concern by, among other things, obtaining additional funding through equity offerings, debt financings and refinancings, collaborations, strategic alliances and/or licensing arrangements. In addition, as we announced on July 11, 2025, our Board is evaluating potential financing transactions, along with strategic alternatives, which may include a potential merger or sale of the Company; in or out of court restructurings; repurchases, redemptions, exchanges or other refinancings of our existing debt; among other potential alternatives. However, there is no assurance that these efforts will result in additional funding, financing transactions, or strategic alternatives.

If we utilize our capital resources more quickly than anticipated or are unable to obtain additional funding or engage in strategic alternatives, we may have to significantly curtail, delay, reduce or eliminate one or more of our research and development programs or any current or future commercialization efforts for one or more of our products or product candidates, which could materially adversely affect our business, financial condition, and results of operations. We may determine to take additional actions to reduce our spending in the near term. As we announced on July 11, 2025, we reduced our workforce by approximately 20% as part of our ongoing careful management of operating expenses. If we are unable to continue as a going concern, we may have to liquidate assets

and may receive less than the value at which those assets are carried on our financial statements. We may also determine to cease operations or file for bankruptcy protection. In any of these circumstances, it is likely that investors will lose all or part of their investment. If there remains substantial doubt about our ability to continue as a going concern, investors or other financing sources may be unwilling to provide funding to us on commercially reasonable terms, if at all. The accompanying condensed consolidated financial statements do not include any adjustments to the carrying amounts and classification of assets and liabilities that may be necessary if we were unable to continue as a going concern.

The significant accounting policies used in preparation of these condensed consolidated financial statements in this Form 10-Q are consistent with those discussed in Note 2, “Summary of Significant Accounting Policies,” in our Annual Report.