fully vested and exercisable. Each Boundless Bio Option outstanding immediately prior to the Effective Time with an exercise price greater than $8.00 will be cancelled for no consideration.

Based on Boundless Bio’s and Serapha’s capitalization as of October 1, 2026 and taking into account Boundless Bio’s current cash position, each share of Serapha Capital Stock is currently estimated to be entitled to receive approximately 8.6737 shares of Boundless Bio Common Stock. This estimated Exchange Ratio does not give effect to the Nasdaq Reverse Split and is subject to adjustment based on estimated Boundless Bio Net Cash (as defined herein) at the Closing as described in more detail in the section titled “The Merger Agreement —Exchange Ratio” beginning on page 192 of the accompanying proxy statement/prospectus.

In connection with the execution and delivery of the Merger Agreement, certain institutional and accredited investors entered into a stock purchase agreement, pursuant to which such persons invested in a private placement of Serapha Series A Preferred Stock, par value $0.00001 per share (the “Serapha Series A Preferred Stock”) for an aggregate purchase price of approximately $138 million. Prior to the closing of the Merger (the “Closing”), certain investors entered into a securities purchase agreement (the “Securities Purchase Agreement”), pursuant to which such persons have agreed to purchase shares of Serapha Common Stock or Serapha Pre-Funded Warrants for an aggregate purchase price of approximately $92 million (the “Serapha Pre-Closing Financing”). The closing of the Serapha Pre-Closing Financing is conditioned upon the satisfaction or waiver of the conditions to the Closing as well as certain other conditions. The Serapha Pre-Closing Financing is more fully described in the accompanying proxy statement/prospectus.

Immediately after the Merger, (i) Boundless Bio securityholders as of immediately prior to the Merger are expected to own approximately 3.8% of the outstanding shares of the Combined Company on a fully-diluted basis, (ii) former Serapha securityholders, excluding shares purchased in the Serapha Pre-Closing Financing, are expected to own approximately 29.3% of the outstanding shares of the Combined Company on a fully-diluted basis, and (iii) shares of Serapha Common Stock and Serapha Pre-Funded Warrants issued in the Serapha Pre-Closing Financing are expected to represent approximately 66.9% of the outstanding shares of capital stock of the Combined Company on a fully-diluted basis, subject to certain assumptions.

Shares of Boundless Bio Common Stock are currently listed on The Nasdaq Global Select Market under the symbol “BOLD.” Boundless Bio has filed an initial listing application for the Combined Company with Nasdaq. After completion of the Merger, Boundless Bio will be renamed “Serapha Bio, Inc.” and it is expected that the Combined Company common stock will trade on Nasdaq under the symbol “AATD.” On     , 2026, the last trading day before the date of the accompanying proxy statement/prospectus, the closing sale price of Boundless Bio Common Stock was $     per share. Under the Merger Agreement, each of Boundless Bio’s and Serapha’s obligation to complete the Merger is subject to the satisfaction or waiver by each of the parties of various conditions, including that the shares of Boundless Bio Common Stock to be issued in the Merger have been approved for listing (subject to official notice of issuance) on Nasdaq as of the Closing. In the event that the shares of Boundless Bio Common Stock to be issued in the Merger are not approved for listing on Nasdaq, it is possible that Boundless Bio and Serapha may mutually agree to waive the applicable condition and nonetheless proceed with completion of the Merger. If such condition is waived, Boundless Bio will not recirculate an updated proxy statement/prospectus, nor will it solicit a new vote of stockholders prior to proceeding with the Merger. Accordingly, you are advised that Boundless Bio stockholders will not have certainty regarding the listing of the Combined Company’s shares at the time you are asked to vote at the special meeting described below.

Boundless Bio stockholders are cordially invited to attend the special meeting of Boundless Bio stockholders. Boundless Bio is holding its special meeting of stockholders (the “Boundless Bio Special Meeting”) on     , 2026, at      Pacific Time, unless postponed or adjourned to a later date, in order to obtain the stockholder approvals necessary to complete the Merger and related matters. The Boundless Bio Special Meeting will be held entirely online via live audio webcast. Please visit www.proxydocs.com/BOLD for more details. You may register to attend the meeting at www.proxydocs.com/BOLD. You will be able to vote online during the meeting. You will need the control number included on your proxy card or on the instructions that accompanied your proxy materials to attend the meeting. At the Boundless Bio Special Meeting, Boundless Bio will ask its stockholders to:

(1) Approve the issuance of shares of Boundless Bio Common Stock (including the shares of Boundless Bio Common Stock issuable upon exercise of the Assumed Warrants and Boundless Bio Pre-Funded Warrants) to stockholders of Serapha pursuant to the terms of the Merger Agreement, a copy of which is attached as Annex A

to the accompanying proxy statement/prospectus, pursuant to which, among other matters, Merger Sub will merge with and into Serapha, with Serapha surviving as a wholly owned subsidiary of Boundless Bio and the surviving corporation of the Merger, which will (i) represent more than 20% of the shares of Boundless Bio Common Stock outstanding immediately prior to the Merger under Nasdaq Listing Rule 5635(a), and (ii) result in a change of control under Nasdaq Listing Rule 5635(b) (the “Nasdaq Stock Issuance Proposal” or “Proposal No. 1”);

(2) Approve an amendment to the amended and restated certificate of incorporation of Boundless Bio (the “Boundless Bio Charter”) to effect a reverse stock split of Boundless Bio’s issued and outstanding common stock at a ratio determined by the board of directors of Boundless Bio (the “Boundless Bio Board of Directors”) and agreed to by Serapha, of one new share of Boundless Bio Common Stock for every    to    shares (or any number in between) of issued and outstanding Boundless Bio Common Stock, in the form attached as Annex B to the accompanying proxy statement/prospectus (the “Nasdaq Reverse Split Proposal” or “Proposal No. 2”);

(3) Approve an amendment to the Boundless Bio Charter to increase the number of shares of Boundless Bio Common Stock that Boundless Bio is authorized to issue from 700,000,000 to    , in the form attached as Annex C to the accompanying proxy statement/prospectus (the “Authorized Share Increase Proposal” or “Proposal No. 3”);

(4) Approve the Serapha Bio, Inc. 2026 Stock Incentive Plan (the “Stock Plan Proposal” or “Proposal No. 4”);

(5) Approve the Serapha Bio, Inc. 2026 Employee Stock Purchase Plan (the “ESPP Proposal” or “Proposal No. 5”);

(6) Approve an adjournment of the Boundless Bio Special Meeting, if necessary, to solicit additional proxies if there are not sufficient votes in favor of Proposal Nos. 1, 2 and 3 (the “Adjournment Proposal” or “Proposal No. 6”); and

(7) Transact such other business as may properly come before the stockholders at the Boundless Bio Special Meeting or any adjournment or postponement thereof.

As described in the accompanying proxy statement/prospectus, certain Boundless Bio stockholders who in the aggregate beneficially owned approximately 1.7% of the outstanding shares of Boundless Bio Common Stock as of June 22, 2026, and certain Serapha stockholders who in the aggregate owned approximately 65.0% of the outstanding shares of Serapha Capital Stock as of June 22, 2026, are parties to stockholder support agreements with Boundless Bio and Serapha whereby such stockholders have agreed to vote in favor of the approval of the transactions contemplated therein, including, with respect to such Serapha stockholders, adoption of the Merger Agreement and approval of the Merger and, with respect to such Boundless Bio stockholders, Proposal Nos. 1, 2 and 3 subject to the terms of the support agreements. Following the effectiveness of the registration statement on Form S-4 of which the accompanying proxy statement/prospectus is a part and pursuant to the Merger Agreement, Serapha stockholders holding a sufficient number of shares of Serapha Capital Stock to adopt the Merger Agreement and approve the Merger and related transactions will be asked to execute written consents providing for such adoption and approval.

Further, prior to the Effective Time, the Boundless Bio Board of Directors expects to declare and set aside the aggregate cash amount to be paid in accordance with a pre-Closing special cash dividend (the “Boundless Bio Pre-Closing Dividend”) to holders of record of outstanding shares of Boundless Bio Common Stock as of a record date prior to the Effective Time, to be set by the Boundless Bio Board of Directors as close as reasonably practicable to (but not later than) the anticipated Closing. The ex-dividend date in respect of such Boundless Bio Pre-Closing Dividend will be determined by Nasdaq. Boundless Bio stockholders of record who continue to hold their eligible shares of Boundless Bio Common Stock until market open on the ex-dividend date will be entitled to payment of the Boundless Bio Pre-Closing Dividend. The Boundless Bio Pre-Closing Dividend will be equal in the aggregate to Boundless Bio’s reasonable, good faith approximation of the amount by which Boundless Bio Net Cash (as determined pursuant to the Merger Agreement) is expected to exceed $0 as of the Closing. The aggregate amount of the Boundless Bio Pre-Closing Dividend is expected to be approximately $44 million to $48 million.

After careful consideration, each of the Boundless Bio Board of Directors and the Serapha Board of Directors has approved the Merger Agreement and have determined that it is advisable to consummate the Merger. The Boundless Bio Board of Directors has approved the proposals described in the accompanying proxy statement/prospectus and recommends that its stockholders vote “FOR” the proposals described in the accompanying proxy statement/prospectus.

More information about Boundless Bio, Serapha, the Merger Agreement and transactions contemplated thereby and the foregoing proposals is contained in the accompanying proxy statement/prospectus. Boundless Bio urges you to read the accompanying proxy statement/prospectus carefully and in its entirety. IN PARTICULAR, YOU SHOULD CAREFULLY CONSIDER THE MATTERS DISCUSSED UNDER “RISK FACTORS” BEGINNING ON PAGE 20 OF THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS.

Boundless Bio and Serapha are excited about the opportunities the Merger brings to Boundless Bio’s and Serapha’s stockholders and thank you for your consideration and continued support. Sincerely,

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the accompanying proxy statement/prospectus. Any representation to the contrary is a criminal offense.

The accompanying proxy statement/prospectus is dated    , 2026, and is first being mailed to Boundless Bio’s stockholders on or about    , 2026.

BOUNDLESS BIO, INC.

11099 North Torrey Pines Road, Suite 150

La Jolla, CA 92037

(858) 766-9912

NOTICE OF SPECIAL MEETING OF BOUNDLESS BIO, INC. STOCKHOLDERS

To the stockholders of Boundless Bio, Inc. (“Boundless Bio”):

NOTICE IS HEREBY GIVEN that a special meeting of stockholders (the “Boundless Bio Special Meeting”) will be held on    , 2026, at    Pacific Time, unless postponed or adjourned to a later date. The Boundless Bio Special Meeting will be held entirely online via live audio webcast. Please visit www.proxydocs.com/BOLD for more details. You may register to attend the meeting at www.proxydocs.com/BOLD. You will be able to vote online during the meeting. You will need the control number included on your proxy card or on the instructions that accompanied your proxy materials to attend the meeting.

The Boundless Bio Special Meeting will be held for the following purposes:

(1) To approve the issuance of shares of common stock of Boundless Bio, par value $0.0001 per share (the “Boundless Bio Common Stock”), (including the shares of Boundless Bio Common Stock issuable upon exercise of Assumed Warrants and Boundless Bio Pre-Funded Warrants) to stockholders of Serapha Bio, Inc. (“Serapha”) pursuant to the terms of the Agreement and Plan of Merger and Reorganization, dated as of June 22, 2026, as amended by Amendment No. 1 to Agreement and Plan of Merger and Reorganization, dated as of August 28, 2026 (as amended, the “Merger Agreement”), by and among Boundless Bio, Serapha and Boulder Merger Sub Corp. (“Merger Sub”), a copy of which is attached as Annex A, pursuant to which, among other matters, Merger Sub will merge with and into Serapha, with Serapha surviving as a wholly owned subsidiary of Boundless Bio and the surviving corporation of the merger (the “Merger”), which will (i) represent more than 20% of the shares of Boundless Bio Common Stock outstanding immediately prior to the Merger under Nasdaq Listing Rule 5635(a), and (ii) result in a change of control under Nasdaq Listing Rule 5635(b);

(2) To approve an amendment to the amended and restated certificate of incorporation of Boundless Bio (the “Boundless Bio Charter”) to effect a reverse stock split of Boundless Bio’s issued and outstanding common stock at a ratio determined by the board of directors of Boundless Bio (the “Boundless Bio Board of Directors”) and agreed to by Serapha, of one new share of Boundless Bio Common Stock for every    to    shares (or any number in between) of issued and outstanding Boundless Bio Common Stock, in the form attached as Annex B;

(3) To approve an amendment to the Boundless Bio Charter to increase the number of shares of Boundless Bio Common Stock that Boundless Bio is authorized to issue from 700,000,000 to    , in the form attached as Annex C;

(4) To approve the Serapha Bio, Inc. 2026 Stock Incentive Plan;

(5) To approve the Serapha Bio, Inc. 2026 Employee Stock Purchase Plan;

(6) To approve an adjournment of the Boundless Bio Special Meeting, if necessary, to solicit additional proxies if there are not sufficient votes in favor of Proposal Nos. 1, 2 and 3; and

(7) To transact such other business as may properly come before the stockholders at the Boundless Bio Special Meeting or any adjournment or postponement thereof.

Record Date: The Boundless Bio Board of Directors has fixed    , 2026 as the record date for the determination of stockholders entitled to notice of, and to vote at, the Boundless Bio Special Meeting and any adjournment or postponement thereof. Only holders of record of shares of Boundless Bio Common Stock at the close of business on the record date are entitled to notice of, and to vote at, the Boundless Bio Special Meeting. At the close of business on the record date, Boundless Bio had    shares of Boundless Bio Common Stock outstanding and entitled to vote.

Your vote is important. The affirmative vote of a majority of the votes properly cast for and against by the holders of Boundless Bio Common Stock at the Boundless Bio Special Meeting, assuming a quorum is present, is required for approval of Proposal Nos. 1, 2, 3, 4, 5 and 6. Approval of each of Proposal No. 1, Proposal No. 2 and Proposal No. 3 is a condition to the completion of the Merger. Therefore, the Merger cannot be consummated without the approval of Proposal Nos. 1, 2 and 3. The approval of Proposal Nos. 4 and 5 are not conditions to the completion of the Merger, however, each of these proposals are conditioned upon the consummation of the Merger and will not be implemented if the Merger is not consummated. Approval of Proposal No. 6 is requested whether or not the Merger is consummated.

Even if you plan to attend the Boundless Bio Special Meeting, Boundless Bio requests that you sign and return the enclosed proxy or vote by mail or online to ensure that your shares will be represented at the Boundless Bio Special Meeting if you are unable to attend. You may change or revoke your proxy at any time before it is voted at the Boundless Bio Special Meeting.

BOUNDLESS BIO’S BOARD OF DIRECTORS HAS DETERMINED AND BELIEVES THAT EACH OF THE PROPOSALS OUTLINED ABOVE IS FAIR TO, IN THE BEST INTERESTS OF, AND ADVISABLE TO BOUNDLESS BIO AND ITS STOCKHOLDERS AND HAS APPROVED EACH SUCH PROPOSAL. BOUNDLESS BIO’S BOARD OF DIRECTORS RECOMMENDS THAT BOUNDLESS BIO STOCKHOLDERS VOTE “FOR” EACH SUCH PROPOSAL.

Important Notice Regarding the Availability of Proxy Materials for the Stockholders’ Meeting to Be Held on    , 2026 at    Pacific Time.

The proxy statement/prospectus in connection with the special meeting is available at www.proxydocs.com/BOLD.

By Order of the Boundless Bio Board of Directors,

Jessica Oien

President, Chief Legal Officer and Corporate Secretary

    , 2026

CERTAIN DEFINED TERMS

The following terms are used throughout this proxy statement/prospectus. Unless stated otherwise, the terms set forth below, whenever used in this proxy statement/prospectus, have the following meanings:

i

ii

iii

iv

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EXPLANATORY NOTE

The issuances of (i) all shares of Boundless Bio Common Stock and Boundless Bio Pre-Funded Warrants, as applicable, in exchange for shares of Serapha Capital Stock (including shares of Serapha Common Stock issued in the Serapha Pre-Closing Financing), (ii) all shares of Boundless Bio Common Stock issuable upon exercise of Boundless Bio Pre-Funded Warrants, (iii) all shares of Boundless Bio Common Stock issuable upon exercise of Assumed Warrants issued in exchange for Serapha Warrants and/or Serapha Pre-Funded Warrants sold in the Serapha Pre-Closing Financing, as applicable, (iv) all Assumed Warrants issued in exchange for Serapha Warrants and Serapha Pre-Funded Warrants, (v) all shares of Boundless Bio Common Stock issuable upon settlement of Assumed RSUs issued in exchange for Serapha RSUs, (vi) all Assumed RSUs issued in exchange for Serapha RSUs, (vii) all Assumed Options issued in exchange for options to purchase shares of Serapha Common Stock, and (viii) all shares of Boundless Bio Common Stock issuable upon exercise of Assumed Options issued in exchange for options to purchase shares of Serapha Common Stock are intended to be covered by this registration statement on Form S-4 of which this proxy statement/prospectus is a part.

There is no difference between (A) the shares of Boundless Bio Common Stock that will be issued in exchange for shares of Serapha Common Stock issued in the Serapha Pre-Closing Financing, (B) the shares of Boundless Bio Common Stock or Boundless Bio Pre-Funded Warrants, as applicable, that will be issued in exchange for other shares of Serapha Capital Stock, (C) the shares of Boundless Bio Common Stock that will be issuable upon exercise of the Boundless Bio Pre-Funded Warrants, (D) the shares of Boundless Bio Common Stock that will be issuable upon the exercise of Assumed Warrants that will be issued in exchange for Serapha Warrants and/or Serapha Pre-Funded Warrants sold in the Serapha Pre-Closing Financing, as applicable, (E) the Assumed Warrants that will be issued in exchange for Serapha Warrants and Serapha Pre-Funded Warrants, (F) the shares of Boundless Bio Common Stock that will be issuable upon the settlement of Assumed RSUs that will be issued in exchange for Serapha RSUs, (G) the Assumed RSUs that will be issued in exchange for Serapha RSUs and (H) the shares of Boundless Bio Common Stock issuable upon exercise of the Assumed Options that will be issued in exchange for options to purchase shares of Serapha Common Stock.

REFERENCES TO ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates important business and financial information about Boundless Bio that is not included in or delivered with this document. You may obtain this information without charge through the SEC website (www.sec.gov) or upon your written or oral request by contacting the Corporate Secretary of Boundless Bio by calling (858) 766-9912 or via email to legal@boundlessbio.com.

To ensure timely delivery of these documents, any request should be made no later than    , 2026 to receive them before the Boundless Bio Special Meeting.

For additional details about where you can find information about Boundless Bio, please see the section titled “Where You Can Find More Information” beginning on page 392 of this proxy statement/prospectus.

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TABLE OF CONTENTS

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QUESTIONS AND ANSWERS ABOUT THE MERGER

Except where specifically noted, the following information and all other information contained in this proxy statement/prospectus does not give effect to the Nasdaq Reverse Split described in Proposal No. 2 of this proxy statement/prospectus.

The following section provides answers to frequently asked questions about the Merger. This section, however, provides only summary information. For a more complete response to these questions and for additional information, please refer to the cross-referenced sections.

For a more complete description of the treatment of Serapha securities in the Merger, please see the sections titled “The Merger Agreement — Merger Consideration,” and “The Merger Agreement — Exchange Ratio” beginning on pages 191 and 192, respectively, of this proxy statement/prospectus. For a description of the effect of the Serapha Pre-Closing Financing on Serapha’s current securityholders, please see the section titled “Agreements Related to the Merger — Securities Purchase Agreement” beginning on page 212 of this proxy statement/prospectus.

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Immediately after the Merger, Boundless Bio securityholders as of immediately prior to the Merger are expected to own approximately 3.8% of the outstanding shares of capital stock of the Combined Company on a fully-diluted basis and former Serapha securityholders are expected to own approximately 96.2% of the outstanding shares of capital stock of the Combined Company on a fully-diluted basis. Under certain circumstances further described in the Merger Agreement, the ownership percentages may be adjusted up or down including, but not limited to, if Boundless Bio Net Cash as of Closing is lower than $0.

In addition, prior to the Effective Time, the Boundless Bio Board of Directors expects to declare the Boundless Bio Pre-Closing Dividend to the pre-Merger Boundless Bio stockholders equal in the aggregate to Boundless Bio’s reasonable, good faith approximation of the amount by which Boundless Bio Net Cash (as determined pursuant to the Merger Agreement) is expected to exceed $0. Boundless Bio management currently estimates that the aggregate amount of cash to be distributed to stockholders of record as of the record date for the Boundless Bio Pre-Closing Dividend will be approximately $44 million to $48 million. If Proposal Nos. 1, 2 and 3, including the Nasdaq Reverse Split Proposal, are approved, Boundless Bio expects to (i) pay the Boundless Bio Pre-Closing Dividend and (ii) effect the Nasdaq Reverse Split following the payment of the Boundless Bio Pre-Closing Dividend and immediately prior to the Closing.

For a more complete description of the treatment of Boundless Bio securities in the Merger, please see the sections titled “The Merger Agreement — Merger Consideration,” “The Merger Agreement — Exchange Ratio,” and “Market Price and Dividend Information” beginning on pages 191, 192 and 19, respectively, of this proxy statement/prospectus.

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Immediately after the Merger, the shares of Serapha Common Stock and Serapha Pre-Funded Warrants issued in the Serapha Pre-Closing Financing are expected to represent approximately 65.83% of the outstanding shares of the Combined Company common stock. Boundless Bio, Serapha and the investors participating in the Serapha Pre-Closing Financing have also agreed to enter into a registration rights agreement at the closing of the Serapha Pre-Closing Financing, pursuant to which, among other things, the Combined Company will agree to provide for the registration and resale of certain shares of Boundless Bio Common Stock that are held by the investors participating in the Serapha Pre-Closing Financing from time to time pursuant to Rule 415. The closing of the Serapha Pre-Closing Financing is conditioned upon the satisfaction or waiver of the conditions to the Closing as well as certain other conditions. The closing of the Serapha Pre-Closing Financing is a condition to the closing of the Merger.

Therefore, Boundless Bio stockholders are being asked to vote on matters related to the Merger without assurance that the proceeds of the Serapha Pre-Closing Financing will be available at the time the Merger is consummated. The investors in the Serapha Pre-Closing Financing have executed binding purchase

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agreements and are obligated to fund their respective commitments at closing, and Serapha would be entitled to pursue specific performance and other contractual remedies to enforce those obligations. However, if the Merger closes before the financing proceeds are received, the Combined Company would initially operate using its then-available cash resources and may need to adjust the timing or scope of certain expenditures until such proceeds are received or alternative capital is obtained.

For a more complete description of the Serapha Pre-Closing Financing, please see the sections titled “Agreements Related to the Merger — Securities Purchase Agreement” and “Agreements Related to the Merger — Registration Rights Agreement” beginning on pages 212 and 214 of this proxy statement/prospectus, respectively.

Approval of each of Proposal Nos. 1, 2 and 3 is a condition to completion of the Merger. The issuance of Boundless Bio Common Stock in connection with the Merger and the change of control resulting from the Merger will not take place unless Proposal Nos. 1, 2 and 3 are approved by Boundless Bio stockholders and the Merger is consummated. The amendment to the Boundless Bio Charter to effect the Nasdaq Reverse Split will not take place unless Proposal No. 2 is approved by the requisite Boundless Bio stockholders; however, Boundless Bio may still elect to proceed with the Nasdaq Reverse Split even if the Merger is not consummated. The amendment to the Boundless Bio Charter to increase the number of authorized shares of Boundless Bio Common Stock will not take place unless Proposal Nos. 1, 2, and 3 are approved by Boundless Bio stockholders and the Merger is consummated.

In addition to the requirement of obtaining Boundless Bio stockholder approval, the Closing is subject to the satisfaction or waiver of each of the other closing conditions set forth in the Merger Agreement. For a more complete description of the closing conditions under the Merger Agreement, please see the section titled “The Merger Agreement — Conditions to the Completion of the Merger” beginning on page 207 of this proxy statement/prospectus.

If Proposal Nos. 1, 2 and 3 are approved, Boundless Bio expects to (i) pay the Boundless Bio Pre-Closing Dividend and (ii) effect the Nasdaq Reverse Split following the payment of the Boundless Bio Pre-Closing Dividend and immediately prior to the Closing. The increase in the number of authorized shares of

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Boundless Bio Common Stock as described in the Authorized Share Increase Proposal would be effected following the Nasdaq Reverse Split and prior to the Closing. The issuance of shares of Boundless Bio Common Stock to stockholders of Serapha pursuant to the terms of the Merger Agreement as described in the Nasdaq Stock Issuance Proposal would be effected on the Closing Date. The Closing is expected to occur by the fourth quarter of 2026 following the satisfaction of all closing conditions. If approved by Nasdaq, the listing of the Combined Company common stock on Nasdaq will take place effective as of the Closing Date.

The presence, in person or being represented by proxy, at the Boundless Bio Special Meeting of the holders of a majority in voting power of Boundless Bio Common Stock outstanding and entitled to vote at the Boundless Bio Special Meeting is necessary to constitute a quorum at the meeting for the purpose of approving the Merger Proposals.

The approvals of Proposal Nos. 4, 5 and 6 are not conditions to the completion of the Merger. The implementation of Proposal Nos. 4 and 5 are each conditioned on the consummation of the Merger. Boundless Bio does not expect that any matter other than the Proposals will be brought before the Boundless Bio Special Meeting.

The presence, in person or being represented by proxy, at the Boundless Bio Special Meeting of the holders of a majority in voting power of Boundless Bio Common Stock outstanding and entitled to vote at the Boundless Bio Special Meeting is necessary to constitute a quorum at the meeting for the purpose of approving the proposals.

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Votes will be counted by the inspector of election appointed for the meeting, who will separately count “FOR” and “AGAINST” votes, abstentions, and broker non-votes, if any. Abstentions and broker non-votes, if any, will be treated as shares present for the purpose of determining the presence of a quorum for the transaction of business at the Boundless Bio Special Meeting, but will not be counted as votes cast and will have no effect on the outcome of the vote for each proposal.

In the case of the Merger, Boundless Bio expects to issue approximately 229.8 million shares of Boundless Bio Common Stock, excluding approximately 415.4 million shares of Boundless Bio Common Stock underlying the Serapha Pre-Funded Warrants and/or shares of Serapha Capital Stock, as applicable, to be exchanged for Assumed Warrants. As of September 30, 2026, there were 23,108,935 shares of Boundless Bio Common Stock outstanding. Therefore, Boundless Bio Common Stock to be issued pursuant to the Merger Agreement (including the shares issued to investors in the Serapha Pre-Closing Financing) will represent greater than 20% of its voting stock outstanding before the issuance.

Accordingly, Boundless Bio is seeking stockholder approval of the issuance of Boundless Bio Common Stock pursuant to the Merger Agreement, including the issuance of Boundless Bio Common Stock underlying the Assumed Warrants exchanged for the Serapha Pre-Funded Warrants issued in the Serapha Pre-Closing Financing and the Boundless Bio Pre-Funded Warrants under the Nasdaq rules.

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On     , 2026, the last trading day before the date of this proxy statement/prospectus, the closing sale price of Boundless Bio Common Stock was $   per share.

Stockholder of Record: Shares Registered in Your Name

If you are a stockholder of record, you may attend the Boundless Bio Special Meeting and vote online during the meeting, vote by proxy over the telephone, vote by proxy through the internet or vote by proxy using a proxy card, the form of which is attached as Annex D to this proxy statement/prospectus. Whether or not you plan to attend the meeting, Boundless Bio urges you to vote by proxy to ensure your vote is counted. You may still attend the meeting and vote during the meeting even if you have already voted by proxy. Please be aware that you must bear any costs associated with your internet access, such as usage charges from Internet access providers and telephone or similar companies.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If you are a beneficial owner of shares registered in the name of your broker, bank, or other agent, you should have received voting instructions from that organization rather than from Boundless Bio. Simply follow the voting instructions provided to ensure that your vote is counted. You may vote by telephone or over the internet as instructed by your broker, bank or other agent. To vote in person at the Boundless Bio Special Meeting, you must contact your broker, bank, or other agent and obtain a valid legal proxy in order to attend, participate in and vote at the Boundless Bio Special Meeting. Follow the voting instructions from your broker, bank or other agent, or contact your broker, bank or other agent for instructions.

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If, on the Record Date, your shares were registered directly in your name with the transfer agent for the Boundless Bio Common Stock then you are a stockholder of record. As a stockholder of record, you may attend the Boundless Bio Special Meeting and vote online during the meeting or vote early by proxy. Whether or not you plan to attend the Boundless Bio Special Meeting, Boundless Bio encourages you to fill out and return your proxy card or vote by proxy over the telephone or on the internet as instructed above to ensure your vote is counted.

If you do not return a proxy card or otherwise vote, your shares will not be voted.

Beneficial Owner: Shares Registered in the Name of a Broker, Fiduciary or Custodian

If you are a beneficial owner of shares registered in the name of your broker, bank or other agent, you should have received voting instructions from that organization rather than from Boundless Bio. Simply follow the voting instructions from that organization to ensure that your vote is counted.

Whether or not you plan to attend the meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend the meeting and vote at the meeting even if you have already voted by proxy.

If you are the beneficial owner and do not direct your broker, fiduciary or custodian how to vote your shares, the question of whether your broker or nominee will still be able to vote your shares depends on whether the New York Stock Exchange (“NYSE”) deems a particular proposal to be a “routine” matter. Your broker, fiduciary or custodian will only be able to vote your shares with respect to proposals considered to be “routine.” Your broker, fiduciary or custodian is not entitled to vote your shares with respect to “non-routine” proposals, resulting in a “broker non-vote” with respect to such proposals. Whether a proposal is considered routine or non-routine is subject to stock exchange rules and final determination by the stock exchange. Even with respect to routine matters, some brokers choose not to exercise their discretionary voting authority. As a result, we urge you to direct your broker, fiduciary or custodian how to vote your shares on all proposals to ensure that your vote is counted.

You may submit a question in advance of the Boundless Bio Special Meeting as a part of the registration process. Questions pertinent to the Boundless Bio Special Meeting and that are submitted in accordance with our rules of conduct for the Boundless Bio Special Meeting will be answered during the Boundless Bio Special Meeting, subject to applicable time constraints. Questions and answers may be grouped by topic and

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substantially similar questions may be grouped and answered once. In order to promote fairness, efficient use of time, and in order to ensure all stockholders are responded to, Boundless Bio will respond to up to two questions from a single stockholder.

YOUR VOTE IS IMPORTANT AND BOUNDLESS BIO STRONGLY ENCOURAGES YOU TO VOTE YOUR SHARES PRIOR TO THE BOUNDLESS BIO SPECIAL MEETING.

Broker non-votes, if any, will be treated as shares present for the purpose of determining the presence of a quorum for the transaction of business at the Boundless Bio Special Meeting. Broker non-votes, if any, will not be counted as “votes properly cast” and will therefore have no effect on Proposal Nos. 1, 2, 3, 4, 5 or 6.

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Your signed proxy card, telephonic proxy instructions, internet proxy instructions, or written notice must be received by    , 2026, 8:59 p.m. Pacific Time to be counted.

If a Boundless Bio stockholder who owns Boundless Bio shares in “street name” has instructed a broker to vote its shares of Boundless Bio Common Stock, the stockholder must follow directions received from its broker to change and/or revoke those instructions.

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MacKenzie Partners, Inc.

7 Penn Plaza, Suite 503

New York, NY 10001

Banks and Brokers call: +1 (212) 929-5500

All others call toll free (U.S. only): +1 (800) 322-2885

Email: proxy@mackenziepartners.com

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RISK FACTORS

The Combined Company will be faced with a market environment that cannot be predicted and that involves significant risks, many of which will be beyond its control. In addition to the other information contained or incorporated by reference in this proxy statement/prospectus, you should carefully consider the material risks described below before deciding how to vote your shares of Boundless Bio Common Stock. You should also read and consider the other information in this proxy statement/prospectus. Please see the section titled “Where You Can Find More Information” beginning on page 392 of this proxy statement/prospectus for further information. Moreover, some of the factors, events and contingencies discussed below may have occurred in the past, but the disclosures below are not representations as to whether or not the factors, events or contingencies have occurred in the past and instead reflect our beliefs and opinions as to the factors, events, or contingencies that could materially and adversely affect us in the future.

Risks Related to the Proposed Merger

Failure to complete, or delays in completing, the potential Merger with Serapha could materially and adversely affect Boundless Bio’s results of operations, business, financial results and/or common stock price.

On June 22, 2026, Boundless Bio entered into the Merger Agreement with Serapha pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Serapha, with Serapha continuing as a wholly owned subsidiary of Boundless Bio and the surviving corporation of the Merger. Completion of the Merger is subject to certain closing conditions, a number of which are not within Boundless Bio’s control. Any failure to satisfy these required conditions to closing may prevent, delay or otherwise materially adversely affect the completion of the transaction. Boundless Bio cannot predict with certainty whether or when any of the required closing conditions will be satisfied or if another uncertainty may arise and cannot assure you that it will be able to successfully complete the Merger as currently contemplated under the Merger Agreement or at all.

Boundless Bio’s efforts to complete the Merger could cause substantial disruptions in, and create uncertainty surrounding, its business, which may materially adversely affect its results of operation and its business. Uncertainty as to whether the Merger will be completed in a timely manner or at all may affect Boundless Bio’s ability to retain and motivate existing employees or could adversely affect Boundless Bio’s business and its relationship with consultants, suppliers, vendors, regulators and other business partners. The adverse effects of the pendency of the transaction could be exacerbated by any delays in completion of the transaction or termination of the Merger Agreement.

If the conditions to the Merger are not satisfied or waived, the Merger may not occur.

Even if the Merger is approved by the stockholders of Serapha and Boundless Bio, specified conditions must be satisfied or, to the extent permitted by applicable law, waived to complete the Merger. These conditions are set forth in the Merger Agreement and described further in the section titled “The Merger Agreement” of this proxy statement/prospectus. Boundless Bio cannot assure you that all of the conditions to the completion of the Merger will be satisfied or waived. If the conditions are not satisfied or waived, the Merger may not occur or the closing may be delayed.

Boundless Bio and Serapha may mutually agree to waive the Nasdaq listing condition under the Merger Agreement, and if such condition is waived, the Combined Company’s stock may not be listed on Nasdaq following completion of the Merger.

Pursuant to the Merger Agreement, Boundless Bio agreed to use commercially reasonable efforts to maintain the listing of Boundless Bio Common Stock on Nasdaq until the Effective Time and, to the extent required by the rules and regulations of Nasdaq, to cause the shares of Boundless Bio Common Stock to be

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issued in connection with the Contemplated Transactions to be approved for listing on Nasdaq. The Merger Agreement also requires the parties, to the extent required by Nasdaq Marketplace Rule 5110, to use commercially reasonable efforts to cause the initial listing application for the Boundless Bio Capital Stock on Nasdaq (including any Boundless Bio Common Stock issuable upon conversion thereof) (the “Nasdaq Listing Application”) to be conditionally approved prior to the Effective Time. Additionally, under the Merger Agreement, each of Boundless Bio’s and Serapha’s obligation to complete the Merger is subject to the satisfaction or waiver by each of the parties of various conditions, including that the Nasdaq Listing Application has been approved by Nasdaq. In the event that the Nasdaq Listing Application is not approved by Nasdaq, it is possible (although not likely) that Boundless Bio and Serapha may mutually agree to waive the applicable condition and nonetheless proceed with completing the Merger. If such condition is waived, Boundless Bio will not recirculate an updated proxy statement/prospectus, nor will it solicit a new vote of stockholders prior to proceeding with the Merger. If Boundless Bio proceeds with the Merger in these circumstances, the Combined Company’s stock may not be listed on Nasdaq.

If the Combined Company’s stock is not listed on Nasdaq following completion of the Merger, trading of the shares could be conducted in the over-the-counter market or on an electronic bulletin board established for unlisted securities such as the Pink Sheets or the OTC Bulletin Board. In such event, it is likely that there would be significantly less liquidity in the trading of the Combined Company common stock, decreases in institutional and other investor demand for the shares, a reduction in coverage by securities analysts, a decrease in market making activity and information available concerning trading prices and volume, and fewer broker dealers willing to execute trades in the Combined Company common stock. Also, it may be difficult for the Combined Company to raise additional capital if the Combined Company common stock is not listed on a major exchange. The occurrence of any of these events could result in a further decline in the market price of the Combined Company common stock and could have a material adverse effect on the Combined Company.

The Exchange Ratio for the Merger will not change or otherwise be adjusted based on the market price of Boundless Bio Common Stock.

Applying the Exchange Ratio, based on Boundless Bio’s and Serapha’s capitalization as of October 1, 2026 and taking into account Boundless Bio’s current cash position, (i) each then-outstanding share of Serapha Capital Stock (including shares of Serapha Common Stock issued in the Serapha Pre-Closing Financing), excluding any shares to be cancelled pursuant to the Merger Agreement, will be converted into the right to receive a number of shares of Boundless Bio Common Stock, equal to 8.6737 shares, (ii) each then-outstanding Serapha Option will be converted into and become an Assumed Option on the existing terms and conditions (including with respect to vesting and accelerated vesting), subject to adjustment as set forth in the Merger Agreement, (iii) each then-outstanding Serapha RSU will be converted into and become an Assumed RSU on the existing terms and conditions (including with respect to vesting and accelerated vesting), subject to adjustments as set forth in the Merger Agreement, and (iv) each then-outstanding Serapha Warrant, including any Serapha Pre-Funded Warrant issued pursuant to the Serapha Pre-Closing Financing, will be converted into an Assumed Warrant, subject to adjustment as set forth in the Merger Agreement and the form of warrant. If the aggregate number of shares of Boundless Bio Common Stock that would otherwise be issued to a holder of Serapha Capital Stock at the Effective Time would exceed such holder’s Beneficial Ownership Limitation, Boundless Bio will issue to such holder shares of Boundless Bio Common Stock up to such holder’s Beneficial Ownership Limitation and, in lieu of the excess shares, Boundless Bio Pre-Funded Warrants to purchase a number of shares of Boundless Bio Common Stock equal to such holder’s Remaining Entitlement. Applying the Exchange Ratio, the former Serapha securityholders immediately before the Merger are expected to own approximately 96.2% of the aggregate number of outstanding shares of the Combined Company’s capital stock following the Merger (on a fully-diluted basis), and Boundless Bio securityholders immediately before the Merger are expected to own approximately 3.8% of the aggregate number of outstanding shares of the Combined Company capital stock following the Merger (on a fully-diluted basis), subject to certain assumptions, including, but not limited to, that Boundless Bio Net Cash as of Closing will be approximately $0, after giving effect to the Boundless Bio Pre-Closing Dividend, which is expected to be approximately $44 million to $48 million.

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Any changes in the market price of Boundless Bio Common Stock before the completion of the Merger will not affect the number of shares Serapha stockholders will be entitled to receive pursuant to the Merger Agreement. However, the Exchange Ratio remains subject to equitable adjustment as set forth in the Merger Agreement for certain changes in the capitalization of Boundless Bio or Serapha, including any stock dividend, subdivision, reclassification, recapitalization, stock split, including the Nasdaq Reverse Split to the extent not previously taken into account in calculating the Exchange Ratio, combination or exchange of shares or other similar change. Therefore, if before the completion of the Merger, the market price of Boundless Bio Common Stock increases from the market price on the date of the Merger Agreement, then Serapha stockholders could receive merger consideration with substantially more value for their shares of Serapha Capital Stock than the parties had negotiated when they established the Exchange Ratio. Similarly, if before the completion of the Merger, the market price of Boundless Bio Common Stock declines from the market price on the date of the Merger Agreement, then Serapha stockholders could receive merger consideration with substantially lower value. The Merger Agreement does not include a price-based termination right.

The issuance of Boundless Bio Common Stock, including the shares of Boundless Bio Common Stock issued in exchange for shares of Serapha Common Stock issued in the Serapha Pre-Closing Financing, to Serapha stockholders pursuant to the Merger Agreement and the resulting change in control from the Merger, and the Nasdaq Reverse Split, must be approved by Boundless Bio stockholders, and the Merger Agreement and transactions contemplated thereby must be approved by the Serapha stockholders. Failure to obtain these approvals would prevent the closing of the Merger.

Before the Merger can be completed, Boundless Bio stockholders must approve, among other things, the Boundless Bio Stockholder Matters, including the issuance of shares of Boundless Bio Common Stock representing (or convertible into) more than 20% of the shares of Boundless Bio Common Stock outstanding immediately prior to the Effective Time to Serapha stockholders in connection with the Contemplated Transactions, the change of control of Boundless Bio resulting from the Contemplated Transactions, the Nasdaq Reverse Split and the increase in authorized shares contemplated by the Boundless Bio Charter Amendments. In addition, Serapha stockholders must adopt the Merger Agreement and approve the Merger and the related transactions. Failure to obtain the required stockholder approvals may result in a material delay in, or the abandonment of, the Merger. Any delay in completing the Merger may materially adversely affect the timing and benefits that are expected to be achieved from the Merger.

The Merger may be completed even though a material adverse effect may result from the announcement of the Merger, industry-wide changes or other causes.

In general, neither Boundless Bio nor Serapha is obligated to complete the Merger if there is a “material adverse effect” (as defined in the Merger Agreement) affecting the other party between June 22, 2026, the date of the Merger Agreement, and the closing of the Merger. However, certain types of causes are excluded from the concept of a “material adverse effect.” Such exclusions include, but are not limited to, changes in general economic or political conditions, industry-wide changes, changes resulting from the announcement of the Merger, natural disasters, pandemics, other public health events or force majeure events and changes in U.S. generally accepted accounting principles. Certain of these exclusions are subject to a limitation and will not apply to the extent Boundless Bio or Serapha, as applicable, is disproportionately affected relative to other similarly situated companies in the industries in which they operate. Therefore, if any of these events were to occur and adversely affect Boundless Bio or Serapha, the adverse effect may not constitute a “material adverse effect” under the Merger Agreement, and the other party may still be required to complete the closing of the Merger notwithstanding such “material adverse effect.” If any such adverse effects occur and Boundless Bio completes the closing of the Merger, the stock price of the Combined Company may suffer. This in turn may reduce the value of the Merger to the stockholders of Boundless Bio, Serapha or both.

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If the Merger is not completed, Boundless Bio’s stock price may decline significantly.

The market price of Boundless Bio Common Stock is subject to significant fluctuations. Market prices for securities of pharmaceutical, biotechnology and other life science companies have historically been particularly volatile. In addition, the market price of Boundless Bio Common Stock will likely be volatile based on whether stockholders and other investors believe that Boundless Bio can complete the Merger or otherwise raise additional capital to support Boundless Bio’s operations if the Merger is not completed and another strategic transaction cannot be identified, negotiated and completed in a timely manner, if at all. The volatility of the market price of Boundless Bio Common Stock has been and may be exacerbated by low trading volume.

Additional factors that may cause the market price of Boundless Bio Common Stock to fluctuate include:

Moreover, the stock markets in general have experienced substantial volatility that has often been unrelated to the operating performance of individual companies. These broad market fluctuations may also adversely affect the trading price of Boundless Bio Common Stock. In the past, following periods of volatility in the market price of a company’s securities, stockholders have often instituted class action securities litigation against such companies.

If Boundless Bio completes the Merger, the Combined Company will need to raise additional capital, including by potentially issuing equity securities or incurring debt, which may cause significant dilution to the Combined Company’s stockholders or restrict the Combined Company’s operations.

In connection with the execution and delivery of the Merger Agreement, Serapha completed the Series A Financing, raising aggregate gross proceeds of approximately $138 million, and has entered into the Securities Purchase Agreement to complete the Serapha Pre-Closing Financing for aggregate gross proceeds of approximately $92 million. The closing of the Serapha Pre-Closing Financing is a condition to the Closing, and the closing of the Serapha Pre-Closing Financing is also conditioned upon satisfaction or waiver of the conditions to the Closing, as well as certain other conditions. The shares of Serapha Common Stock and the Serapha Pre-Funded Warrants issued in the Serapha Pre-Closing Financing will result in dilution to all securityholders of the Combined Company (i.e., both Boundless Bio’s pre-Merger securityholders and former Serapha securityholders).

Additional or alternative financing may not be available to the Combined Company when it is needed or may not be available on favorable terms. To the extent that the Combined Company raises additional capital by issuing equity securities, such financing will cause additional dilution to all securityholders of the Combined Company, including Boundless Bio’s pre-Merger securityholders and Serapha’s former securityholders. It is also possible that the terms of any new equity securities may have preferences over the Combined Company common stock. Any debt financing the Combined Company enters into may involve covenants that restrict its operations.

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These restrictive covenants may include limitations on additional borrowing and specific restrictions on the use of the Combined Company’s assets, as well as prohibitions on its ability to create liens, pay dividends, redeem its stock or make investments. In addition, if the Combined Company raises additional funds through licensing arrangements, it may be necessary to grant licenses on terms that are not favorable to the Combined Company.

Some of Boundless Bio’s and Serapha’s directors and executive officers have interests in the Merger that are different from yours and that may influence them to support or approve the Merger without regard to your interests.

Directors and executive officers of Boundless Bio and Serapha have interests in the Merger that are different from, or in addition to, the interests of other Boundless Bio stockholders generally. These interests with respect to Boundless Bio’s directors and executive officers may include, among others, retention bonus payments, acceleration of previously issued equity awards, severance payments if employment is terminated in a qualifying termination in connection with the Merger and rights to continued indemnification, expense advancement and insurance coverage.

Further, certain current members of the Serapha Board of Directors will continue as directors of the Combined Company after the Effective Time, and, following the closing of the Merger, will be eligible to be compensated as non-employee directors of the Combined Company pursuant to Boundless Bio’s non-employee director compensation policy that is expected to remain in place following the Effective Time. These interests, among other factors, may have influenced the directors and executive officers of each company to support or approve the Merger.

The Boundless Bio Board of Directors was aware of and considered those interests, among other matters, in reaching their decisions to approve and adopt the Merger Agreement, approve the Merger, and recommend the approval of the Merger Agreement to Boundless Bio stockholders. These interests, among other factors, may have influenced the directors and executive officers of each company to support or approve the Merger.

Boundless Bio stockholders and Serapha stockholders may not realize a benefit from the Merger commensurate with the ownership dilution they will experience in connection with the Merger, including the conversion of Serapha Common Stock issued in the Serapha Pre-Closing Financing.

If the Combined Company is unable to realize the full strategic and financial benefits currently anticipated from the Merger, Boundless Bio stockholders and Serapha stockholders will have experienced substantial dilution of their ownership interests without receiving any commensurate benefit, or only receiving part of the commensurate benefit to the extent the Combined Company is able to realize only part of the strategic and financial benefits currently anticipated from the Merger.

Boundless Bio securityholders will generally have a reduced ownership and voting interest in, and will exercise less influence over the management of, the Combined Company following the completion of the Merger as compared to their current ownership and voting interests in the respective companies.

After the completion of the Merger, Boundless Bio’s current stockholders will generally own a smaller percentage of the Combined Company than their ownership of Boundless Bio prior to the Merger. Immediately after the Merger, Boundless Bio securityholders as of immediately prior to the Merger are expected to own approximately 3.8% of the outstanding shares of capital stock of the Combined Company (on a fully-diluted basis), and former holders of Serapha securities are expected to own approximately 96.2% of the outstanding shares of capital stock of the Combined Company (on a fully-diluted basis), subject to certain assumptions, including, but not limited to, Boundless Bio Net Cash as of closing being approximately $0, after giving effect to the Boundless Bio Pre-Closing Dividend, which is expected to be approximately $44 million to $48 million. The Chief Executive Officer of Serapha will serve as the Chief Executive Officer of the Combined Company following the completion of the Merger.

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Certain provisions of the Merger Agreement may discourage third parties from submitting competing proposals, including proposals that may be superior to the transactions contemplated by the Merger Agreement.

While the Merger Agreement is in effect, each of Boundless Bio and Serapha is generally prohibited from, among other things, soliciting, initiating or knowingly encouraging, inducing or facilitating the communication, making, submission or announcement of any acquisition proposal or acquisition inquiry. In addition, Boundless Bio’s current directors and executive officers have entered into support agreements pursuant to the terms of the Merger Agreement, and as an inducement to Serapha’s willingness to enter into the Merger Agreement, by which they have agreed to vote all of their shares of Boundless Bio Capital Stock in favor of the Contemplated Transactions and against any competing proposals, subject to certain limited exceptions. These provisions could discourage a potential competing acquirer from considering or proposing an acquisition or merger, even if it were prepared to pay consideration with a higher value than that implied by the merger consideration in the combination.

Because the lack of a public market for Serapha Common Stock makes it difficult to evaluate the fair market value of its capital stock, the value of Boundless Bio Common Stock to be issued to Serapha stockholders may be more or less than the fair market value of Serapha Common Stock.

The outstanding capital stock of Serapha is privately held and is not traded on any public market. The lack of a public market makes it difficult to determine the fair market value of Serapha Capital Stock. Because the percentage of Boundless Bio’s equity to be issued to Serapha stockholders was determined based on negotiations between the parties, it is possible that the value of Boundless Bio Common Stock to be issued to Serapha stockholders will be more or less than the fair market value of Serapha Capital Stock.

Lawsuits may be filed against Boundless Bio, Serapha, or any of the members of their respective boards of directors arising out of the Merger, which may delay or prevent the Merger.

Putative stockholder complaints, including stockholder class action complaints, and other complaints may be filed against Boundless Bio, the Boundless Bio Board of Directors, Serapha, the Serapha Board of Directors and others in connection with the transactions contemplated by the Merger Agreement. The outcome of litigation is uncertain, and Boundless Bio or Serapha may not be successful in defending against any such future claims. Lawsuits that may be filed against Boundless Bio, the Boundless Bio Board of Directors, Serapha, or the Serapha Board of Directors could delay or prevent the Merger, divert the attention of Boundless Bio’s and Serapha’s management and employees from their day-to-day business and otherwise adversely affect Boundless Bio and Serapha financially.

Boundless Bio has never paid and, other than in connection with the Merger with Serapha, does not intend to pay any cash dividends in the foreseeable future.

Boundless Bio has never paid cash dividends on any of its capital stock. Other than the Boundless Bio Pre-Closing Dividend in connection with the Merger, Boundless Bio does not currently anticipate declaring or paying cash dividends on its capital stock in the foreseeable future.

The amount of the Boundless Bio Pre-Closing Dividend may change based on the timing to complete the Merger, changes in operating expense levels and other factors.

The Boundless Bio Pre-Closing Dividend, which is expected to be approximately $44 million to $48 million, is based on Boundless Bio’s estimate of the amount by which Boundless Bio Net Cash, as determined pursuant to the terms of the Merger Agreement, will exceed $0. The actual amount of the Boundless Bio Pre-Closing Dividend may be higher or lower than the estimated amount and is subject to change based on the timing to complete the Merger, changes in Boundless Bio’s operating expense levels, transaction-related costs and expenses, and other adjustments to the components of Boundless Bio Net Cash as set forth in the Merger Agreement. There can be no assurance that the actual amount of the Boundless Bio Pre-Closing Dividend will not materially differ from the current estimate.

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If Boundless Bio does not successfully complete the Merger or another strategic transaction, the Boundless Bio Board of Directors may decide to pursue a dissolution and liquidation of Boundless Bio. In such an event, the amount of cash available for distribution to Boundless Bio stockholders will depend heavily on the timing of such liquidation as well as the amount of cash that will need to be reserved for commitments and contingent liabilities, as to which Boundless Bio can give you no assurance.

There can be no assurance that the Merger will be completed. If the Merger is not completed, the Boundless Bio Board of Directors may decide to pursue a dissolution and liquidation of Boundless Bio. In such an event, the amount of cash available for distribution to Boundless Bio stockholders will depend heavily on the timing of such decision and, ultimately, such liquidation, since the amount of cash available for distribution continues to decrease as Boundless Bio funds its operations while pursuing the Merger. In addition, if the Boundless Bio Board of Directors were to approve and recommend, and Boundless Bio stockholders were to approve, a dissolution and liquidation of Boundless Bio, Boundless Bio would be required under Delaware law to pay Boundless Bio’s outstanding obligations, as well as to make reasonable provision for contingent and unknown obligations, prior to making any distributions in liquidation to stockholders. Boundless Bio’s commitments and contingent liabilities may include obligations under Boundless Bio’s employment and related agreements with certain employees that provide for severance and other payments following a termination of employment occurring for various reasons, including a change in control of Boundless Bio, litigation against Boundless Bio, and other various claims and legal actions arising in the ordinary course of business, and other unexpected and/or contingent liabilities. As a result of this requirement, a portion of Boundless Bio’s assets would need to be reserved pending the resolution of such obligations.

In addition, Boundless Bio may be subject to litigation or other claims related to a dissolution and liquidation of Boundless Bio. If a dissolution and liquidation were to be pursued, the Boundless Bio Board of Directors, in consultation with Boundless Bio’s advisors, would need to evaluate these matters and make a determination about a reasonable amount to reserve. Accordingly, holders of Boundless Bio Common Stock could lose all or a significant portion of their investment in the event of liquidation, dissolution or winding up of Boundless Bio. A liquidation would be a lengthy and uncertain process with no assurance of any value ever being returned to Boundless Bio stockholders.

Boundless Bio and its stockholders will not have any right to make damage claims against Serapha for the breach of any representation, warranty or covenant made by Serapha in the Merger Agreement.

The Merger Agreement provides that all of the representations, warranties and covenants of the parties contained therein shall not survive the Closing, except for those covenants contained therein that by their terms survive the Closing. Accordingly, there are no remedies available to the parties with respect to any breach of the representations, warranties, covenants or agreements of the parties to the Merger Agreement after the Closing, except for covenants that by their terms survive the Closing. As a result, Boundless Bio and its stockholders will have no remedy available to it if the Merger is completed and it is later revealed that there was a breach of any of the representations, warranties and covenants made by Serapha at the time of the Merger.

Additionally, Boundless Bio cannot assure you that the due diligence conducted in relation to Serapha has identified all material issues or risks associated with Serapha, its business or the industry in which it competes. Furthermore, Boundless Bio cannot assure you that factors outside of its or Serapha’s control will not later arise, or that any previously identified risks will not materialize in a manner inconsistent with the preliminary analysis. As a result of these factors, following the Closing, the Combined Company may be exposed to liabilities and incur additional costs and expenses and it may be forced to later write-down or write off assets, restructure its operations, or incur impairment or other charges. Boundless Bio and its stockholders have no indemnification rights against Serapha or its stockholders under the Merger Agreement. Accordingly, any stockholders of Boundless Bio that remain stockholders of the Combined Company following the Merger could suffer a reduction in the value of their securities. Such stockholders are unlikely to have a remedy for such reduction in value unless they are able to successfully claim that the reduction was due to the breach by Boundless Bio’s

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directors or officers of a duty of care or other fiduciary duty owed to them, or if they are able to successfully bring a private claim under securities laws that the registration statement or proxy statement/prospectus relating to the Merger contained an actionable material misstatement or material omission.

The Beam Litigation is not expected to be resolved prior to the completion of the Merger, and Boundless Bio stockholders will be asked to vote on the Merger Proposals without knowing its outcome.

The Beam Litigation, described under “Risk Factors — Risks Related to Serapha” and “Serapha’s Business — Legal Proceedings,” is at an early stage and is not expected to be resolved before the Boundless Bio Special Meeting or the Closing. Following the Merger, the Combined Company, whose business will be focused on SERP-01, will bear the costs of the Beam Litigation and the consequences of any adverse outcome. The Exchange Ratio will not be adjusted to reflect the pendency or outcome of the Beam Litigation, and Boundless Bio and its stockholders will not have any right to indemnification from Serapha or its stockholders for losses arising from the Beam Litigation. Accordingly, Boundless Bio stockholders should carefully consider the risks associated with the Beam Litigation in deciding how to vote on the proposals described in this proxy statement/prospectus.

Risks Related to the Proposed Nasdaq Reverse Split

The Nasdaq Reverse Split may not increase the Combined Company’s stock price over the long-term.

The principal purpose of the Nasdaq Reverse Split is to increase the per-share market price of Boundless Bio Common Stock above the minimum bid price requirement under the Nasdaq rules so that the listing of Boundless Bio and the shares of Boundless Bio Common Stock being issued in the Merger on Nasdaq will be approved. Based on the recent trading prices of Boundless Bio Common Stock, Boundless Bio and Serapha currently estimate that a reverse stock split ratio of at least 1-for-    would be required to increase the per-share market price to $4.00, which is the minimum initial listing price requirement of Nasdaq. The final reverse stock split ratio will be determined mutually by the Boundless Bio Board of Directors and the Serapha Board of Directors prior to the Closing based primarily on the then-current trading price of Boundless Bio Common Stock and the objective of achieving a post-closing per-share price that (1) satisfies Nasdaq’s listing requirements and (2) provides an appropriate and sustainable post-closing per-share market price that the parties believe will better position the Combined Company for long-term trading stability, investor interest and market visibility, taking into account prevailing market conditions and other relevant factors. Accordingly, the ratio effected is likely to be greater than the minimum necessary to satisfy Nasdaq’s listing standards. It cannot be assured, however, that the Nasdaq Reverse Split will accomplish this objective for any meaningful period of time. While it is expected that the reduction in the number of outstanding shares of common stock will proportionally increase the market price of Boundless Bio Common Stock, it cannot be assured that the Nasdaq Reverse Split will increase the market price of its common stock by a multiple of the reverse stock split ratio mutually agreed by Boundless Bio and Serapha, or result in any permanent or sustained increase in the market price of Boundless Bio Common Stock, which is dependent upon many factors, including Boundless Bio’s business and financial performance, general market conditions and prospects for future success. Thus, while the stock price of Boundless Bio might meet the listing requirements for Nasdaq initially, it cannot be assured that it will continue to do so.

The Nasdaq Reverse Split may decrease the liquidity of the Combined Company common stock.

Although the Boundless Bio Board of Directors believes that the anticipated increase in the market price of the Combined Company common stock resulting from the proposed Nasdaq Reverse Split could encourage interest in its common stock and possibly promote greater liquidity for its stockholders, such liquidity could also be adversely affected by the reduced number of shares outstanding after the Nasdaq Reverse Split. The reduction in the number of outstanding shares may lead to reduced trading and a smaller number of market makers for the Combined Company common stock. In addition, the Nasdaq Reverse Split may not result in an increase in the Combined Company’s stock price necessary to satisfy Nasdaq’s initial listing requirements for the Combined Company.

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The Nasdaq Reverse Split may lead to a decrease in the Combined Company’s overall market capitalization.

Should the market price of the Combined Company common stock decline after the Nasdaq Reverse Split, the percentage decline may be greater, due to the smaller number of shares outstanding, than it would have been prior to the Nasdaq Reverse Split. A reverse stock split is often viewed negatively by the market and, consequently, can lead to a decrease in the Combined Company’s overall market capitalization. If the per share market price does not increase in proportion to the reverse stock split ratio, then the value of the Combined Company, as measured by its stock capitalization, will be reduced. In some cases, the per-share stock price of companies that have effected reverse stock splits subsequently declined back to pre-reverse split levels, and accordingly, it cannot be assured that the total market value of the Combined Company common stock will remain the same after the Nasdaq Reverse Split is effected, or that the Nasdaq Reverse Split will not have an adverse effect on the Combined Company’s stock price due to the reduced number of shares outstanding after the Nasdaq Reverse Split.

Risks Related to Boundless Bio

Risks Related to Boundless Bio’s Limited Operating History, Financial Position and Capital Requirements

Boundless Bio has a limited operating history, has incurred significant operating losses since its inception, and expects to incur significant losses for the foreseeable future. Boundless Bio may never generate any revenue or become profitable or, if it achieves profitability, Boundless Bio may not be able to sustain it.

Biopharmaceutical product development is a highly speculative undertaking and involves a substantial degree of risk. Boundless Bio is a clinical-stage oncology company with a limited operating history upon which you can evaluate its business and prospects. Boundless Bio commenced operations in 2018, has no products approved for commercial sale, and has not generated any revenue from the sale of its products. To date, Boundless Bio has focused primarily on organizing and staffing the company, business planning, raising capital, building its proprietary Spyglass platform, discovering its extrachromosomal DNA (“ecDNA”) directed therapeutic candidates (“ecDTx”), developing its diagnostic, establishing its intellectual property portfolio, conducting research, preclinical studies and clinical trials, establishing arrangements with third parties for the manufacture of its ecDTx and supply of related raw materials, and providing general and administrative support for these operations. Boundless Bio’s scientific approach to the discovery and development of ecDTx, including its use of the Spyglass platform, is unproven, and Boundless Bio does not know whether it will be able to develop or obtain regulatory approval for any products of commercial value. In May 2025, Boundless Bio announced that it discontinued the monotherapy arm and combination arms of BBI-355 with third-party targeted therapies in the POTENTIATE trial based on initial trial data. Boundless Bio had been continuing to investigate BBI-355 in combination with BBI-825; however, in January 2026, following a strategic portfolio review, Boundless Bio elected to cease enrollment of the POTENTIATE trial due to market considerations, clinical data, and prioritization of its BBI-940 program and will no longer invest in the development of ECHO, which is an ecDNA diagnostic clinical trial assay used in the POTENTIATE trial. In June 2026, Boundless Bio announced that based on preliminary exposure data obtained in the early dose escalation cohorts of the KOMODO-1 clinical trial, Boundless Bio believed that the observed pharmacokinetic exposure data did not support continued clinical development of BBI-940. Boundless Bio has not yet completed any clinical trials, successfully developed and validated a diagnostic test, obtained regulatory approvals, manufactured products at commercial scale, or arranged for a third party to do so on its behalf, or conducted sales or marketing activities necessary for successful product commercialization. Consequently, any predictions made about Boundless Bio’s future success or viability may not be as accurate as they could be if Boundless Bio had a history of successfully developing and commercializing biopharmaceutical products.

Boundless Bio has incurred significant operating losses since its inception and expects to incur significant losses for the foreseeable future. Boundless Bio does not have any products approved for sale and has not generated any revenue since its inception. If the Merger is not completed and Boundless Bio continues to develop any current or future ecDTx and Boundless Bio is unable to successfully develop, obtain requisite approval for

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and commercialize any current or future ecDTx, Boundless Bio may never generate revenue. Boundless Bio’s net losses were $58.2 million and $65.4 million for the years ended December 31, 2025 and 2024, respectively. As of June 30, 2026, Boundless Bio had an accumulated deficit of $296.9 million. Substantially all of Boundless Bio’s losses have resulted from expenses incurred in connection with its research and development programs and from general and administrative costs associated with its operations. All of Boundless Bio’s current or future ecDTx will require substantial additional development time and resources before Boundless Bio would be able to apply for or receive regulatory approvals and begin generating revenue from product sales. Boundless Bio expects to continue to incur losses for the foreseeable future, and Boundless Bio anticipates these losses will increase substantially if the Merger is not completed and Boundless Bio continues to develop any current or future ecDTx, seek regulatory approval for, and potentially commercialize any current or future ecDTx and seek to discover and develop additional ecDTx, as well as operate as a public company.

If the Merger is not completed, to become and remain profitable, Boundless Bio must succeed in discovering, developing, obtaining regulatory approvals for, and eventually commercializing products that generate significant revenue. This will require Boundless Bio to be successful in a range of challenging activities, including completing clinical trials and preclinical studies of its ecDTx, discovering additional ecDTx, obtaining regulatory approval for these ecDTx and, if required, its diagnostic, and manufacturing, marketing, and selling any products for which Boundless Bio may obtain regulatory approval. Boundless Bio is in only the preliminary stages of these activities. Boundless Bio may never succeed in these activities and, even if it does, may never generate revenue that is significant enough to achieve profitability. In addition, Boundless Bio has not yet demonstrated an ability to successfully overcome many of the risks and uncertainties frequently encountered by companies in new and rapidly evolving fields, particularly in the biopharmaceutical industry. Because of the numerous risks and uncertainties associated with biopharmaceutical product development, Boundless Bio is unable to accurately predict the timing or amount of increased expenses or when, or if, Boundless Bio will be able to achieve profitability. Even if Boundless Bio does achieve profitability, it may not be able to sustain or increase profitability on a quarterly or annual basis. Boundless Bio’s failure to become and remain profitable may have an adverse effect on the value of Boundless Bio and could impair its ability to raise capital, expand its business, maintain its research and development efforts, diversify its ecDTx pipeline, achieve its strategic objectives, or even continue its operations. A decline in the value of Boundless Bio could also cause you to lose all or part of your investment.

Boundless Bio will require substantial additional capital to finance its operations if the Merger is not completed and it continues to develop any ecDTx, and a failure to obtain this necessary capital when needed on acceptable terms, or at all, could force Boundless Bio to delay, limit, reduce, or terminate any ecDTx development programs, commercialization efforts, or other operations.

The development of Boundless Bio’s ecDTx, including conducting preclinical studies and clinical trials, is a very time-consuming, capital-intensive, and uncertain process. Boundless Bio’s operations have consumed substantial amounts of cash since inception. If Boundless Bio continues to develop any ecDTx, Boundless Bio expects its expenses to substantially increase in connection with any ongoing activities, particularly if it conducts any clinical trials and preclinical studies and potentially seeks regulatory approval for any current or future ecDTx it may develop. If Boundless Bio obtains regulatory approval for its ecDTx or any future ecDTx it may develop, Boundless Bio also expects to incur significant commercialization expenses related to product manufacturing, marketing, sales, and distribution. Because the outcome of any clinical trial or preclinical study is highly uncertain, Boundless Bio cannot reasonably estimate the actual amount of capital necessary to successfully complete the development and commercialization of its ecDTx. Furthermore, Boundless Bio will continue to incur additional costs associated with operating as a public company.

Based on its current operating plan, Boundless Bio believes that its existing cash, cash equivalents, and short-term investments will be sufficient to fund its operations through the anticipated closing date of the Merger and for a period of at least 12 months from the date of issuance of its unaudited interim financial statements for the quarter ended June 30, 2026 appearing elsewhere in this proxy statement/prospectus. Boundless Bio has based its belief in this regard on assumptions that may prove to be wrong, and it could expend its capital

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resources sooner than currently expected. Boundless Bio’s operating plans and other demands on its cash resources may change as a result of many factors currently unknown, and Boundless Bio may need to seek additional funds sooner than planned. Boundless Bio’s existing capital is not sufficient to complete development of its current or future ecDTx, and Boundless Bio will require substantial capital in order to advance any current or future ecDTx through clinical trials, regulatory approval, and commercialization. Accordingly, if the Merger is not completed, Boundless Bio will need to obtain substantial additional funding in connection with its continuing operations. Boundless Bio’s ability to raise additional funds may be adversely impacted by global economic conditions, disruptions to, and volatility in, the credit and financial markets in the United States, inflation, diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates, and uncertainty about economic stability. If Boundless Bio is unable to complete the Merger, its ability to raise additional funds and the terms upon which it is able to raise such funds may also be adversely affected by the uncertainties regarding its financial condition, uncertainties with respect to the prospects for its ecDTx programs, the sufficiency of its capital resources, potential future management turnover, and volatility and instability in the global financial markets. As a result of these and other factors, there is no guarantee that sufficient additional funding will be available to Boundless Bio on acceptable terms, or at all. If the equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult, more costly, and more dilutive. If Boundless Bio is unable to raise capital when needed or on attractive terms and Boundless Bio continues to develop any ecDTx, Boundless Bio could be forced to delay, reduce, or eliminate its research and development programs or any future commercialization efforts, or even cease operations. If the Merger is not completed, Boundless Bio expects to finance its cash needs through public or private equity or debt financings or other capital sources, including potential collaborations, licenses, and other similar arrangements. In addition, Boundless Bio may seek additional capital due to favorable market conditions or strategic considerations even if it believes it has sufficient funds for its current or future operating plans. Attempting to secure additional financing may divert Boundless Bio’s management from its day-to-day activities, which may adversely affect its ability to develop its ecDTx.

Boundless Bio currently has a “shelf” registration statement on Form S-3 effective and an existing at-the-market (“ATM”) offering program; however, its ability to raise capital under its shelf registration statement, including through the ATM offering program, may be limited by SEC rules and regulations. Based on Boundless Bio’s public float as of the filing date of this proxy statement/prospectus, as calculated pursuant to SEC rules, Boundless Bio is only permitted to utilize its shelf registration statement, including the prospectus pursuant to which its ATM offering is conducted, subject to Instruction I.B.6 of Form S-3, which is referred to as the “baby shelf” rule. Accordingly, for so long as Boundless Bio’s public float is less than $75.0 million, it generally may not sell securities registered on its shelf registration statement in a primary offering with a value exceeding more than one-third of its public float during any 12 calendar month period. Although alternative public and private transaction structures may be available to raise additional capital, these may require additional time and cost, may impose operational restrictions on Boundless Bio, and may not be available on acceptable terms.

Boundless Bio’s future capital requirements are difficult to predict and will depend on many factors, including, but not limited to:

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Conducting clinical trials and preclinical studies and discovering potential ecDTx is a time-consuming, expensive, and uncertain process that takes years to complete, and Boundless Bio may never generate the necessary data or results required to obtain regulatory approval and commercialize its ecDTx. In addition, Boundless Bio’s ecDTx, if approved, may not achieve commercial success. Boundless Bio’s commercial revenue, if any, will initially be derived from sales of products that it does not expect to be commercially available for many years, if at all.

Accordingly, if the Merger is not completed and Boundless Bio continues to develop any ecDTx, Boundless Bio will need to continue to rely on additional financing to achieve its business objectives. Adequate additional financing may not be available to Boundless Bio on acceptable terms, or at all, including as a result of financial and credit market deterioration or instability, market-wide liquidity shortages, geopolitical events, or otherwise.

Raising additional capital may cause dilution to Boundless Bio’s stockholders, restrict its operations, or require Boundless Bio to relinquish rights to its technologies or ecDTx.

Until Boundless Bio can generate substantial product revenue, if ever, and if the Merger is not completed, it expects to finance its cash needs through equity offerings, debt financings, or other capital sources, including potential collaborations, licenses, and other similar arrangements. Boundless Bio does not have any committed external source of funds. To the extent that Boundless Bio raises additional capital through the sale of equity or convertible debt securities, existing stockholders’ ownership interest may be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect their rights as common stockholders. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting Boundless Bio’s ability to take specific actions, such as incurring additional debt, making capital expenditures, or declaring dividends. Such restrictions could adversely impact Boundless Bio’s ability to conduct its operations and execute its business plan.

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If Boundless Bio raises additional funds through future collaborations, licenses, and other similar arrangements, Boundless Bio may be required to relinquish valuable rights to its future revenue streams or proprietary technology, or grant licenses on terms that may not be favorable to Boundless Bio and/or that may reduce the value of Boundless Bio Common Stock. If Boundless Bio is unable to raise additional funds through equity or debt financings or other arrangements when needed or on terms acceptable to it, Boundless Bio would be required to delay, limit, reduce, or terminate any product development or future commercialization efforts, or grant rights to develop and market ecDTx that it might otherwise prefer to develop and market itself, or on less favorable terms than it would otherwise choose.

Risks Related to the Discovery, Development, and Regulatory Approval of Boundless Bio’s ecDTx

If Boundless Bio continues to develop any ecDTx and is unable to successfully develop, obtain regulatory approval, and ultimately commercialize any current or future ecDTx, or experiences significant delays in doing so, its business will be materially harmed.

Boundless Bio has invested substantially all of its efforts to date in developing its ecDTx, developing a diagnostic as a potential patient selection tool, identifying other targets for therapeutic pursuit, and developing its proprietary Spyglass platform. If Boundless Bio continues to develop any ecDTx, there can be no assurance any current or future ecDTx will demonstrate acceptable or commercially viable clinical trial results. Boundless Bio’s ability to generate product revenue, which it does not expect will occur for many years, if ever, will depend heavily on the successful development and eventual commercialization of its ecDTx. The success of Boundless Bio’s ecDTx will depend on several factors, including the following:

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If Boundless Bio is unable to develop, obtain regulatory approval for, or, if approved, successfully commercialize any ecDTx, or if Boundless Bio experiences delays as a result of any of the above factors or otherwise, its business would be materially harmed.

Boundless Bio’s approach to treating cancer with oncogene amplifications by developing ecDTx directed against ecDNA is novel and unproven, and if Boundless Bio continues to develop any ecDTx, Boundless Bio does not know whether it will be able to develop any products of commercial value, or if competing approaches will limit the commercial value of its ecDTx.

The success of Boundless Bio’s business depends primarily upon its ability to discover, develop, and commercialize products based on its scientific approach, which is focused on developing therapies that are directed against ecDNA in oncogene amplified cancers, a novel and unproven approach. While Boundless Bio has had favorable preclinical study results for certain of its ecDTx programs, Boundless Bio has not yet succeeded and may not succeed in demonstrating efficacy and safety for its ecDTx in clinical trials or in obtaining regulatory approvals from the FDA or other regulatory authorities or in commercializing such ecDTx. For example, in May 2025, Boundless Bio announced that it discontinued the monotherapy arm and combination arms of BBI-355 with third-party targeted therapies in the POTENTIATE trial based on initial trial data. Boundless Bio had been continuing to investigate BBI-355 in combination with BBI-825; however, in January 2026, following a strategic portfolio review, Boundless Bio elected to cease enrollment of the POTENTIATE trial due to market considerations, clinical data, and prioritization of its BBI-940 program and will no longer invest in the development of ECHO, which is an ecDNA diagnostic clinical trial assay used in the POTENTIATE trial. In June 2026, Boundless Bio announced that based on preliminary exposure data obtained in the early dose escalation cohorts of the KOMODO-1 clinical trial, Boundless Bio believed that the observed pharmacokinetic exposure data did not support continued clinical development of BBI-940. As an organization, Boundless Bio has not completed any clinical trials for any of its ecDTx. If Boundless Bio continues to develop any ecDTx, Boundless Bio’s research methodology and scientific approach in using its Spyglass platform may be unsuccessful in identifying and discovering additional ecDTx, and, even if successful, Boundless Bio may not be able to submit INDs and have such INDs allowed to proceed to enable it to commence clinical trials on the timelines it expects, if at all. Any ecDTx Boundless Bio does discover may be shown to have harmful side effects or may have other characteristics that may necessitate additional clinical testing or make the ecDTx unmarketable or unlikely to receive regulatory approval. In particular, developing therapies that are directed against ecDNA in oncogene amplified cancers is a novel approach that may have unexpected consequences, including adverse events that preclude successful development and approval of Boundless Bio’s ecDTx. Further, because Boundless Bio’s ecDTx and all of its discovery programs are ecDNA based, adverse developments with respect to one of its programs may have a significant adverse impact on the actual or perceived likelihood of success and value of its other programs.

In addition, the biotechnology and biopharmaceutical industries are characterized by rapidly advancing technologies. If Boundless Bio continues to develop any ecDTx, Boundless Bio’s future success will depend in part on its ability to maintain a competitive position with its scientific approach. If Boundless Bio fails to stay at the forefront of technological change in utilizing its approach to create and develop ecDTx and, if required, diagnostic tests, Boundless Bio may be unable to compete effectively. Boundless Bio’s competitors may render its approach obsolete or limit the commercial value of its products or ecDTx by advances in existing technological approaches or the development of new or different approaches, potentially eliminating the

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advantages in its drug discovery process that Boundless Bio believes it derives from its approach. By contrast, adverse developments with respect to other companies that attempt to use a similar approach to Boundless Bio’s approach may adversely impact the actual or perceived value and potential of its ecDTx.

If any of these events occur, Boundless Bio may be forced to delay, modify, or abandon its development efforts for a program or programs, which would have a material adverse effect on its business and could potentially cause Boundless Bio to cease operations.

Clinical and preclinical development involves a lengthy and expensive process with uncertain timelines and outcomes, and the results of preclinical studies and early clinical trials are not necessarily predictive of future results. If Boundless Bio continues to develop any ecDTx, Boundless Bio’s ecDTx may not achieve favorable results in ongoing or future clinical trials or preclinical studies or receive regulatory approval on a timely basis, if at all.

Clinical and preclinical development is expensive and can take many years to complete, and its outcome is inherently uncertain. If Boundless Bio continues to develop any ecDTx, Boundless Bio cannot guarantee that any clinical trials or preclinical studies will be conducted as planned, including whether it is able to meet expected timeframes for data readouts, or completed on schedule, if at all, and failure can occur at any time during the trial or study process. Despite any promising preclinical or clinical results, any ecDTx can unexpectedly fail at any stage of clinical or preclinical development. The historical failure rate for product candidates in the industry is high, particularly in the earlier stages of development. For example, as discussed above, in May 2025, Boundless Bio announced that it discontinued the monotherapy arm and combination arms of BBI-355 with third-party targeted therapies in the POTENTIATE trial based on initial trial data. Boundless Bio had been continuing to investigate BBI-355 in combination with BBI-825; however, in January 2026, following a strategic portfolio review, Boundless Bio elected to cease enrollment of the POTENTIATE trial due to market considerations, clinical data, and prioritization of its BBI-940 program and will no longer invest in the development of ECHO, which is an ecDNA diagnostic clinical trial assay used in the POTENTIATE trial. In June 2026, Boundless Bio announced that based on preliminary exposure data obtained in the early dose escalation cohorts of the KOMODO-1 clinical trial, Boundless Bio believed that the observed pharmacokinetic exposure data did not support continued clinical development of BBI-940. The results from preclinical studies or clinical trials of an ecDTx or of a competitor’s product candidates in the same class may not predict the results of later clinical trials of Boundless Bio’s current or future ecDTx, and interim, topline, or preliminary results of a clinical trial are not necessarily indicative of final results. ecDTx in later stages of clinical trials may fail to show the desired safety and efficacy characteristics despite having progressed through preclinical studies and initial clinical trials. It is not uncommon to observe results in clinical trials that are unexpected based on preclinical studies and early clinical trials, and many product candidates fail in clinical trials despite very promising early results. If unexpected observations or toxicities are observed in these studies, or in future IND-enabling studies for Boundless Bio’s current and any potential future ecDTx development programs, such results may delay or prevent the initiation of clinical trials for such ecDTx programs.

Moreover, preclinical and clinical data may be susceptible to varying interpretations and analyses. A number of companies in the biopharmaceutical and biotechnology industries, including Boundless Bio, as discussed above, have suffered significant setbacks in clinical development even after achieving promising results in earlier studies. Such setbacks have occurred and may occur for many reasons if Boundless Bio continues to develop any ecDTx, including, but not limited to: clinical sites and investigators may deviate from clinical trial protocols, whether due to lack of training or otherwise, and Boundless Bio may fail to detect any such deviations in a timely manner; patients may fail to adhere to any required clinical trial procedures, including any requirements for post-treatment follow-up; any current or future ecDTx may fail to demonstrate effectiveness or safety in certain patient subpopulations, which has not been observed in earlier trials due to limited sample size, lack of analysis, or otherwise; or Boundless Bio’s clinical trials may not adequately represent the patient populations it intends to treat, whether due to limitations in its trial designs or otherwise, such as where one patient subgroup is overrepresented in the clinical trial. Based upon negative or inconclusive results, Boundless

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Bio or any future collaborator may decide, or regulators may require Boundless Bio, to conduct additional preclinical studies or clinical trials, which would cause Boundless Bio to incur additional operating expenses and delays and may not be sufficient to support regulatory approval on a timely basis or at all.

As a result, if Boundless Bio continues to develop any ecDTx, Boundless Bio cannot be certain that its clinical trials and preclinical studies will be successful. Any safety concerns observed in any one of Boundless Bio’s clinical trials in its targeted indications could limit the prospects for regulatory approval of its ecDTx in those and other indications, which could have a material adverse effect on Boundless Bio’s business, financial condition, results of operations, and prospects.

If Boundless Bio continues to develop any ecDTx, any difficulties or delays in the commencement or completion, or the termination or suspension, of its clinical trials or preclinical studies could result in increased costs to Boundless Bio, delay or limit its ability to generate revenue, or adversely affect its commercial prospects.

Before obtaining marketing approval from regulatory authorities for the sale of Boundless Bio’s ecDTx, Boundless Bio must conduct extensive clinical trials to demonstrate the safety and efficacy of the ecDTx in humans. Before Boundless Bio can initiate clinical trials for its preclinical ecDTx, it must submit the results of preclinical studies to the FDA or comparable foreign regulatory authorities along with other information, including information about ecDTx chemistry, manufacturing, and controls, and its proposed clinical trial protocol, as part of an IND or similar regulatory submission. The FDA or comparable foreign regulatory authorities may require Boundless Bio to conduct additional preclinical studies for any ecDTx before it allows Boundless Bio to initiate clinical trials under any IND or similar regulatory submission, which may lead to delays and increase the costs of Boundless Bio’s preclinical ecDTx programs. Moreover, even if Boundless Bio commences clinical trials, issues may arise that could cause regulatory authorities to suspend or terminate such clinical trials. Any such delays in the commencement or completion, or the termination or suspension, of Boundless Bio’s clinical trials or preclinical studies for its current and any future ecDTx could significantly affect its product development timelines and product development costs.

If Boundless Bio continues to develop any ecDTx, Boundless Bio does not know whether its clinical trials and preclinical studies will begin on time or if its ongoing or future trials or studies will be completed on schedule, if at all. The commencement, data readouts, and completion of clinical trials and preclinical studies can be delayed for a number of reasons, including delays related to:

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Clinical trials must be conducted in accordance with the FDA and other applicable regulatory authorities’ legal requirements, regulations, or guidelines, and are subject to oversight by these governmental agencies and ECs or IRBs at the medical institutions where the clinical trials are conducted. Boundless Bio could also encounter delays if a clinical trial is suspended or terminated by Boundless Bio, by ECs or IRBs of the institutions in which such trials are being conducted, by a data safety monitoring board for such trial or by the FDA or comparable foreign regulatory authorities. Such authorities may impose such a suspension or termination due to a number of factors, including failure to conduct the clinical trial in accordance with GCP and other regulatory requirements or Boundless Bio’s clinical protocols, inspection of the clinical trial operations or trial site by the FDA or comparable foreign regulatory authorities resulting in the imposition of a clinical hold, unforeseen safety issues or adverse side effects, failure to demonstrate a benefit from using a drug, changes in governmental regulations, or administrative actions or lack of adequate funding to continue the clinical trial. In addition, changes in regulatory requirements and policies may occur, and Boundless Bio may need to amend clinical trial protocols to comply with these changes. Amendments may require Boundless Bio to resubmit Boundless Bio’s clinical trial protocols to ECs or IRBs for reexamination, which may impact the costs, timing, or successful completion of a clinical trial.

Further, if Boundless Bio conducts clinical trials in foreign countries, this will present additional risks that may delay completion of Boundless Bio’s clinical trials. These risks include the failure of enrolled patients in foreign countries to adhere to clinical protocols as a result of differences in healthcare services or cultural customs, managing additional administrative burdens associated with foreign regulatory schemes, and political and economic risks, including war, relevant to such foreign countries.

Moreover, principal investigators for Boundless Bio’s clinical trials may serve as scientific advisors or consultants to Boundless Bio from time to time and receive compensation in connection with such services.

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Under certain circumstances, Boundless Bio may be required to report some of these relationships to the FDA or comparable foreign regulatory authorities. The FDA or comparable foreign regulatory authority may conclude that a financial relationship between Boundless Bio and a principal investigator has created a conflict of interest or otherwise affected interpretation of the study. The FDA or comparable foreign regulatory authority may therefore question the integrity of the data generated at the applicable clinical trial site and the utility of the clinical trial itself may be jeopardized. This could result in a delay in approval, or rejection, of Boundless Bio’s marketing applications by the FDA or a comparable foreign regulatory authority, as the case may be, and may ultimately lead to the denial of regulatory approval of Boundless Bio’s ecDTx.

In addition, many of the factors that cause, or lead to, the termination or suspension of, or a delay in the commencement or completion of, clinical trials may also ultimately lead to the denial of regulatory approval of an ecDTx. Any delays to Boundless Bio’s clinical trials that occur as a result could shorten any period during which Boundless Bio may have the exclusive right to commercialize Boundless Bio’s ecDTx. In such cases, Boundless Bio’s competitors may be able to bring products to market before Boundless Bio does, and the commercial viability of Boundless Bio’s ecDTx could be significantly reduced. Any of these occurrences may harm Boundless Bio’s business, financial condition, results of operations, and prospects.

If Boundless Bio continues to develop any ecDTx, Boundless Bio may find it difficult to enroll patients in any clinical trials. If Boundless Bio encounters difficulties or delays enrolling patients in Boundless Bio’s clinical trials, Boundless Bio’s clinical development activities could be delayed or otherwise adversely affected.

Successful and timely completion of clinical trials will require that Boundless Bio identifies and enrolls a specified number of patients for each of Boundless Bio’s clinical trials. Boundless Bio may not be able to initiate or continue clinical trials for any ecDTx if Boundless Bio is unable to identify and enroll a sufficient number of eligible patients to participate in these trials as required by the FDA or similar regulatory authorities outside the United States. Patient enrollment, a significant factor in the timing of clinical trials, is affected by many factors, including the size and characteristics of the patient population, the proximity of patients to clinical sites, the eligibility and exclusion criteria for the trial, the design of the clinical trial, the risk that enrolled patients will not complete a clinical trial, Boundless Bio’s ability to recruit clinical trial investigators with the appropriate competencies and experience, and competing clinical trials and clinicians’ and patients’ perceptions as to the potential advantages and risks of any ecDTx being studied in relation to other available therapies, including any new products that may be approved for the indications Boundless Bio may be investigating as well as any product candidates under development. Boundless Bio will be required to identify and enroll a sufficient number of patients for each of Boundless Bio’s clinical trials and monitor such patients adequately during and after treatment. Potential patients for any planned clinical trials may not be adequately diagnosed or identified with the diseases that Boundless Bio is targeting, which could adversely impact the outcomes of Boundless Bio’s trials and could have safety concerns for the potential patients. Potential patients for any planned clinical trials may also not meet the entry criteria for such trials.

In particular, because Boundless Bio’s ecDTx are focused on patients with tumors harboring oncogene amplifications on or enabled by ecDNA, Boundless Bio’s ability to enroll eligible patients may be limited or take more time than Boundless Bio anticipates, due to the frequency of the biomarker Boundless Bio is seeking to target, or Boundless Bio’s ability to effectively identify such biomarker. Boundless Bio also may encounter difficulties in identifying and enrolling patients with the proper tumor characteristics or stage of disease appropriate for any of Boundless Bio’s clinical trials and monitoring such patients adequately during and after treatment. Additionally, other pharmaceutical companies targeting these same types of cancer are recruiting clinical trial patients from these patient populations, which may make it more difficult to fully enroll Boundless Bio’s clinical trials. The timing of Boundless Bio’s clinical trials depends, in part, on the speed at which Boundless Bio can recruit patients to participate in Boundless Bio’s trials, as well as completion of required follow-up periods. The eligibility criteria of Boundless Bio’s clinical trials, once established, may further limit the pool of available trial participants. If patients are unwilling or unable to participate in Boundless Bio’s trials

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for any reason, including the existence of concurrent clinical trials for similar target populations, the availability of approved therapies, or the fact that enrolling in Boundless Bio’s trials may prevent patients from taking a different product, or Boundless Bio otherwise has difficulty enrolling a sufficient number of patients, the timeline for recruiting patients, conducting trials, and obtaining regulatory approval of Boundless Bio’s current or future ecDTx may be delayed. Additionally, patients in Boundless Bio’s prior clinical trials are typically in the late stages of their disease and may experience disease progression independent from Boundless Bio’s ecDTx, making them unevaluable for purposes of the clinical trial and requiring additional patient enrollment. Boundless Bio’s inability to enroll a sufficient number of patients for any of Boundless Bio’s future clinical trials would result in significant delays or may require Boundless Bio to abandon one or more clinical trials altogether.

In addition, if Boundless Bio continues to develop any ecDTx, Boundless Bio will continue to rely on CROs and clinical trial sites to ensure proper and timely enrollment of Boundless Bio’s clinical trials. Though Boundless Bio has entered into agreements governing their services, Boundless Bio has limited influence over their actual performance. Boundless Bio cannot assure you that Boundless Bio’s assumptions used in determining expected clinical trial timelines are correct, or that Boundless Bio will not experience delays or difficulties in enrollment, or be required by the FDA or other regulatory authorities to increase Boundless Bio’s enrollment, which would result in the delay of completion of such trials beyond Boundless Bio’s expected timelines.

Use of Boundless Bio’s current or future ecDTx could be associated with side effects, adverse events, or other properties or safety risks, which could delay or preclude regulatory approval, cause Boundless Bio to suspend or discontinue clinical trials, cause Boundless Bio to abandon an ecDTx, limit the commercial profile of an approved label, or result in other significant negative consequences that could severely harm Boundless Bio’s business, financial condition, results of operations, and prospects.

As is the case with oncology drugs generally, it is likely that there may be side effects and adverse events associated with use of Boundless Bio’s ecDTx. If Boundless Bio continues to develop any ecDTx, results of Boundless Bio’s clinical trials could reveal a high and unacceptable severity and prevalence of expected or unexpected side effects or unexpected characteristics. Undesirable side effects caused by any of Boundless Bio’s ecDTx when used alone or in combination with approved or investigational drugs could cause Boundless Bio or regulatory authorities to interrupt, delay, or halt clinical trials and could result in a more restrictive label, or lead to the delay or denial of regulatory approval by the FDA or comparable foreign regulatory authorities. The drug-related side effects could affect patient recruitment or the ability of enrolled patients to complete the trial or result in potential product liability claims. Any of these occurrences may harm Boundless Bio’s business, financial condition, results of operations, and prospects significantly.

Moreover, if Boundless Bio’s ecDTx are associated with undesirable side effects in clinical trials or demonstrate characteristics that are unexpected, Boundless Bio may elect to abandon their development or limit their development to more narrow uses or subpopulations in which the undesirable side effects or other characteristics are less prevalent, less severe, or more acceptable from a risk-benefit perspective, which may limit the commercial expectations for the ecDTx if approved. Unacceptable enhancement of certain toxicities may be seen when Boundless Bio’s ecDTx is combined with standard of care therapies, or when used as a single agent. Boundless Bio may also be required to modify Boundless Bio’s development and clinical trial plans based on findings in Boundless Bio’s ongoing clinical trials. For example, in the now-discontinued monotherapy arm of the POTENTIATE trial, BBI-355 administered with continuous every other day dosing (“Q2D”) demonstrated a narrow therapeutic index resulting from hematological toxicity at or near doses associated with clinical activity, and in the now-discontinued combination arms with third-party targeted therapies, the combination of BBI-355 administered with Q2D dosing in combination with these therapies was not well-tolerated at the exposure levels believed to be required for robust, sustained anti-tumor activity. Many compounds that initially showed promise in early-stage testing for treating cancer have later been found to cause side effects that prevented further development of the compounds. In addition, if Boundless Bio continues to develop any ecDTx, Boundless Bio plans to study its ecDTx in combination with other therapies, which may exacerbate adverse events associated with such ecDTx.

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If Boundless Bio continues to develop any ecDTx and successfully completes early phase clinical studies and establishes initial clinical proof-of-concept, it is possible that as Boundless Bio tests its ecDTx in larger, longer, and more extensive clinical trials, including with different dosing regimens, or as the use of these ecDTx becomes more widespread following any regulatory approval, more illnesses, injuries, discomforts, and other adverse events than were observed in earlier trials, as well as new conditions that did not occur or went undetected in previous trials, may be discovered. If such side effects become known later in development or upon approval, if any, such findings may harm Boundless Bio’s business, financial condition, and prospects significantly.

Patients treated with Boundless Bio’s current or future ecDTx may also be undergoing surgical, radiation, and/or chemotherapy treatments, which can cause side effects or adverse events that are unrelated to Boundless Bio’s ecDTx but may still impact the success of Boundless Bio’s clinical trials. The inclusion of critically ill patients in Boundless Bio’s clinical trials may result in deaths or other adverse medical events due to other therapies or medications that such patients may be using or due to the gravity of such patients’ illnesses. For example, if Boundless Bio continues to develop any ecDTx, Boundless Bio expects that some of the patients enrolled in its clinical trials will die or experience major clinical events either during the course of Boundless Bio’s clinical trials or after participating in such trials.

In addition, if Boundless Bio’s ecDTx receives regulatory approval, and Boundless Bio or others later identify undesirable side effects caused by such product, a number of potentially significant negative consequences could result, including:

Any of these events could prevent Boundless Bio from achieving or maintaining market acceptance of the particular ecDTx, if approved, and could significantly harm Boundless Bio’s business, results of operations, and prospects.

As an organization, Boundless Bio has never completed any clinical trials and may be unable to do so if Boundless Bio continues to develop any ecDTx.

Boundless Bio has never completed any clinical trials, and if Boundless Bio continues to develop any ecDTx, Boundless Bio will need to successfully complete ongoing and later-stage and pivotal clinical trials in order to obtain FDA or comparable foreign regulatory approval to market any current or future ecDTx. Carrying out later-stage clinical trials and the submission of a successful NDA is a complicated process. As discussed above, Boundless Bio elected to cease enrollment in the POTENTIATE trial and has not yet completed any clinical trials for Boundless Bio’s ecDTx. Boundless Bio has limited experience as a company in preparing and submitting marketing applications and has not previously submitted an NDA or other comparable foreign

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regulatory submission for any ecDTx. In addition, as a company, Boundless Bio has had limited interactions with the FDA and no interaction with other comparable foreign regulatory authorities and cannot be certain how many additional clinical trials of Boundless Bio’s ecDTx will be required or how such trials should be designed. Consequently, Boundless Bio may be unable to successfully and efficiently execute and complete necessary clinical trials in a way that leads to submission and regulatory approval of Boundless Bio’s ecDTx. Boundless Bio may require more time and incur greater costs than its competitors and may not succeed in obtaining regulatory approvals of ecDTx that Boundless Bio may develop. Failure to commence or complete, or delays in, any of Boundless Bio’s clinical trials could prevent Boundless Bio from or delay Boundless Bio in submitting marketing applications, including NDAs, for and commercializing its ecDTx.

If Boundless Bio continues to develop any ecDTx and is unable to successfully identify predictive biomarkers to identify patient populations most likely to benefit from Boundless Bio’s ecDTx, or develop a diagnostic to enable patient selection for Boundless Bio’s ecDTx, or if Boundless Bio experiences significant delays in doing so, Boundless Bio may not realize the full commercial potential of its ecDTx.

If Boundless Bio continues to develop any ecDTx, a key component of Boundless Bio’s strategy will continue to be its ability to identify patient populations most likely to benefit from its ecDTx by using a biomarker-driven approach. Identification of these patients will require identification of predictive biomarkers and may require the development and use of a diagnostic assay.

Boundless Bio may not be able to identify predictive biomarkers to identify patients most likely to benefit from its ecDTx. If Boundless Bio identifies predictive biomarkers, there are several risks associated with the development of a diagnostic assay to identify the biomarkers. Boundless Bio may not be able to validate a diagnostic and the related biomarkers or their functional relevance clinically. Potential biomarkers, even if validated preclinically, may not be functionally validated in human clinical trials. Any failure by Boundless Bio to successfully develop or obtain marketing authorization for a diagnostic assay, or any delays in doing so, may harm the commercial prospects of its ecDTx. Moreover, Boundless Bio may need to work with a third-party diagnostic developer to assist it in developing a diagnostic assay. For example, Boundless Bio developed an ecDNA diagnostic called ECHO as a clinical trial assay for use during its Phase 1/2 POTENTIATE clinical trial using a third-party in vitro diagnostic company, although, following its strategic portfolio review in January 2026 and its decision to cease enrollment of the POTENTIATE trial, Boundless Bio will no longer invest in the development of ECHO. In the future, Boundless Bio may have difficulty identifying or maintaining a relationship with a third-party diagnostic developer, and it may face competition from other companies in establishing these relationships.

If Boundless Bio continues to develop any ecDTx, Boundless Bio may develop its ecDTx in combination with other therapies, which exposes Boundless Bio to additional risks.

If Boundless Bio continues to develop any ecDTx, Boundless Bio may develop its ecDTx for use in combination with one or more currently approved cancer therapies. Even if its ecDTx was to receive regulatory approval or be commercialized for use in combination with other existing therapies, Boundless Bio would continue to bear the risks that the FDA or similar foreign regulatory authorities could revoke approval of the therapy used in combination with its ecDTx or that safety, efficacy, manufacturing, or supply issues could arise with these existing therapies. Combination therapies are commonly used for the treatment of cancer, and Boundless Bio would be subject to similar risks if Boundless Bio develops its ecDTx for use in combination with other drugs or biologics or for indications other than cancer. Developing combination therapies using approved therapeutics, as Boundless Bio may do for its ecDTx, also exposes Boundless Bio to additional clinical risks, such as the requirement that Boundless Bio demonstrate the safety and efficacy of each active component of any combination regimen it may develop.

If the FDA or similar foreign regulatory authorities revoke the approval of combination agents, or if safety, efficacy, manufacturing, or supply issues arise with the drugs Boundless Bio chooses to evaluate in combination with Boundless Bio’s ecDTx, Boundless Bio may be unable to obtain approval of or market Boundless Bio’s ecDTx for combination therapy regimens.

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Additionally, if the third-party providers of therapies or therapies in development used in combination with its ecDTx are unable to produce sufficient quantities for clinical trials or for commercialization of Boundless Bio’s ecDTx, or if the cost of combination therapies are prohibitive, Boundless Bio’s development and commercialization efforts would be impaired, which would have an adverse effect on Boundless Bio’s business, financial condition, results of operations, and prospects.

Boundless Bio may expend Boundless Bio’s limited resources to pursue a particular ecDTx or a particular indication for an ecDTx and fail to capitalize on ecDTx or indications that may be more profitable or for which there is a greater likelihood of success.

Because Boundless Bio has limited financial and managerial resources, if Boundless Bio continues to develop any ecDTx, Boundless Bio may focus on specific ecDTx, development programs, and indications. As a result, Boundless Bio may forgo or delay pursuit of opportunities with other ecDTx that could have had greater commercial potential. Boundless Bio’s resource allocation and other decisions may cause Boundless Bio to fail to identify and capitalize on viable potential ecDTx or additional indications for its ecDTx or other profitable market opportunities. Boundless Bio’s spending on current and future research and development programs and ecDTx for specific indications may not yield any commercially viable ecDTx.

In addition, if Boundless Bio does not accurately evaluate the commercial potential or target market for a particular indication or ecDTx, Boundless Bio may relinquish valuable rights to that ecDTx through collaborations, licenses, and other similar arrangements in cases in which it would have been more advantageous for Boundless Bio to retain sole development and commercialization rights to such ecDTx.

If Boundless Bio continues to develop any ecDTx, it may in the future conduct certain of its clinical trials for Boundless Bio’s ecDTx outside of the United States. However, the FDA and other foreign equivalents may not accept data from such trials, in which case Boundless Bio’s development plans will be delayed, which could materially harm Boundless Bio’s business.

If Boundless Bio continues to develop any ecDTx, Boundless Bio may in the future conduct one or more of Boundless Bio’s clinical trials for Boundless Bio’s ecDTx outside the United States. The acceptance of study data from clinical trials conducted outside the United States or another jurisdiction by the FDA or comparable foreign regulatory authority may be subject to certain conditions or may not be accepted at all. In cases where data from foreign clinical trials are intended to serve as the sole basis for regulatory approval in the United States, the FDA will generally not approve the application on the basis of foreign data alone unless the data are applicable to the United States population and United States medical practice; the trials were performed by clinical investigators of recognized competence and pursuant to GCP regulations; and the data may be considered valid without the need for an on-site inspection by the FDA, or if the FDA considers such inspection to be necessary, the FDA is able to validate the data through an on-site inspection or other appropriate means. In addition, even where the foreign study data are not intended to serve as the sole basis for approval, if the relevant study was not conducted pursuant to an IND, the FDA will not accept the data as support for a marketing application unless the study was conducted in accordance with GCP requirements and the FDA is able to validate the data from the study through an onsite inspection if deemed necessary. Many foreign regulatory authorities have similar requirements for clinical data gathered outside of their respective jurisdictions. There can be no assurance the FDA will accept data from clinical trials conducted outside of the United States. If the FDA does not accept data from Boundless Bio’s clinical trials of its ecDTx, it would likely result in the need for additional clinical trials, which would be costly and time-consuming and delay or permanently halt Boundless Bio’s development of its ecDTx.

Conducting clinical trials outside the United States also exposes Boundless Bio to additional risks, including risks associated with:

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If Boundless Bio continues to develop any ecDTx, interim, topline, and preliminary data from Boundless Bio’s clinical trials and preclinical studies that Boundless Bio announces or publishes from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data.

From time to time, Boundless Bio may publicly disclose interim, topline, or preliminary data from its clinical trials and preclinical studies, which is based on a preliminary analysis of then-available data, and the results and related findings and conclusions are subject to change following a more comprehensive review of the data related to the particular study or trial. Boundless Bio also makes assumptions, estimations, calculations, and conclusions as part of Boundless Bio’s analyses of data, and Boundless Bio may not have received or had the opportunity to fully and carefully evaluate all data. As a result, the interim, topline, or preliminary results that Boundless Bio reports may differ from future results of the same studies or trials, or different conclusions or considerations may qualify such results once additional data have been received and fully evaluated. Topline and preliminary data also remain subject to audit and verification procedures that may result in the final data being materially different from the topline or preliminary data Boundless Bio previously published. As a result, topline and preliminary data should be viewed with caution until the final data are available. Interim data from clinical trials that Boundless Bio may complete are further subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more patient data become available. Adverse differences between interim, topline, or preliminary data and final data could significantly harm Boundless Bio’s business prospects.

In addition, others, including regulatory authorities, may not accept or agree with Boundless Bio’s assumptions, estimates, calculations, conclusions, or analyses or may interpret or weigh the importance of data differently, which could impact the value of the particular program, the approvability or commercialization of the particular ecDTx or product and its company in general. Moreover, the information Boundless Bio chooses to publicly disclose regarding a particular study or clinical trial is based on what is typically extensive information, and you or others may not agree with what Boundless Bio determines is material or otherwise appropriate information to include in its disclosure, and any information Boundless Bio determines not to disclose may ultimately be deemed significant with respect to future decisions, conclusions, views, activities or otherwise regarding a particular drug, ecDTx or its business. If the interim, topline, or preliminary data that Boundless Bio report differ from actual results, or if others, including regulatory authorities, disagree with the conclusions reached, Boundless Bio’s ability to obtain approval for, and commercialize its ecDTx may be harmed, which could harm Boundless Bio’s business, operating results, prospects, or financial condition.

Changes in methods of ecDTx manufacturing or formulation may result in additional costs or delay.

As any of Boundless Bio’s current or future ecDTx progress through preclinical studies to clinical trials to regulatory approval and commercialization, it is common that various aspects of the ecDTx development program, such as manufacturing methods and formulation, are altered along the way in an effort to optimize safety, efficacy, yield, and manufacturing batch size, minimize costs, and achieve consistent quality and results. There can be no assurance that this or any other future manufacturing or formulation changes will achieve their intended objectives. These changes and any future changes Boundless Bio may make to its ecDTx may also cause such candidates to perform differently and affect the results of future clinical trials conducted with the altered materials. Such changes or related unfavorable clinical trial results could delay initiation or completion of

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additional clinical trials, require the conduct of bridging studies or clinical trials or the repetition of one or more studies or clinical trials, increase development costs, delay or prevent potential regulatory approval, and jeopardize Boundless Bio’s ability to commercialize its ecDTx, if approved, and generate revenue.

If Boundless Bio is required by the FDA or comparable foreign regulatory authority to obtain approval of a companion diagnostic test in connection with approval of Boundless Bio’s ecDTx, and Boundless Bio does not obtain, or face delays in obtaining, FDA or foreign approval of such companion diagnostic, Boundless Bio will not be able to commercialize Boundless Bio’s ecDTx, and Boundless Bio’s ability to generate revenue will be materially impaired.

If the FDA believes that the safe and effective use of Boundless Bio’s ecDTx depends on an in vitro diagnostic, then it may require approval or clearance of that diagnostic as a companion diagnostic at the same time that the FDA approves its ecDTx, if at all. According to FDA guidance, if the FDA determines that a companion diagnostic device is essential to the safe and effective use of a novel therapeutic product or indication, the FDA generally will not approve the therapeutic product or new therapeutic product indication if the companion diagnostic is not also approved or cleared for that indication. If a diagnostic is not commercially available in this situation, Boundless Bio may be required to complete the development of a diagnostic that would be subject to regulatory approval requirements. The process of obtaining or creating such diagnostics is time-consuming and costly.

Companion diagnostics are developed in conjunction with clinical programs for the associated product and are subject to regulation as medical devices by the FDA and comparable foreign regulatory authorities, and the FDA has generally required premarket approval of companion diagnostics for cancer therapies. As such, Boundless Bio expects that if it continues to develop any ecDTx, it may need to obtain approval for any diagnostic Boundless Bio may develop for use with its ecDTx. The approval or clearance of a companion diagnostic as part of the therapeutic product’s further labeling limits the use of the therapeutic product to only those patients who express the specific characteristic that the companion diagnostic was developed to detect.

If the FDA or a comparable foreign regulatory authority requires approval or clearance of a companion diagnostic for its ecDTx, whether before, simultaneously with, or after the ecDTx obtains regulatory approval, Boundless Bio and/or third-party developers may encounter difficulties in developing and obtaining approval or clearance for these companion diagnostics. Any delay or failure by Boundless Bio or third-party developers to develop or obtain regulatory approval or clearance of a companion diagnostic could delay or prevent approval or continued marketing of the relevant ecDTx. Boundless Bio or its third-party developers may also experience delays in developing a sustainable, reproducible, and scalable manufacturing process for the companion diagnostic or in transferring that process to commercial partners or negotiating insurance reimbursement plans, all of which may prevent Boundless Bio from completing any clinical trials or commercializing its ecDTx, if approved, on a timely or profitable basis, if at all. Following its strategic portfolio review in January 2026 and its decision to cease enrollment of the POTENTIATE trial, Boundless Bio will no longer invest in the development of ECHO, which is an ecDNA diagnostic clinical trial assay used in the POTENTIATE trial.

Boundless Bio may attempt to secure approval from the FDA through the use of the accelerated approval pathway if Boundless Bio continues to develop any ecDTx. If Boundless Bio is unable to obtain such approval, Boundless Bio may be required to conduct additional clinical trials beyond those that Boundless Bio contemplates, which could increase the expense of obtaining, and delay the receipt of, necessary regulatory approvals. Even if Boundless Bio receives accelerated approval from the FDA, if its confirmatory trials do not verify clinical benefit, or if Boundless Bio does not comply with rigorous post-marketing requirements, the FDA may seek to withdraw any accelerated approval it had obtained.

If Boundless Bio continues to develop any ecDTx, Boundless Bio may in the future seek an accelerated approval for Boundless Bio’s ecDTx. Under the accelerated approval program, the FDA may grant accelerated approval to a product candidate designed to treat a serious or life-threatening condition that provides meaningful

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therapeutic benefit over available therapies upon a determination that the product candidate has an effect on a surrogate endpoint or intermediate clinical endpoint that is reasonably likely to predict clinical benefit. The FDA considers a clinical benefit to be a positive therapeutic effect that is clinically meaningful in the context of a given disease, such as irreversible morbidity or mortality. For the purposes of accelerated approval, a surrogate endpoint is a marker, such as a laboratory measurement, radiographic image, physical sign, or other measure that is thought to predict clinical benefit, but is not itself a measure of clinical benefit. An intermediate clinical endpoint is a clinical endpoint that can be measured earlier than an effect on irreversible morbidity or mortality that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit.

The accelerated approval pathway may be used in cases in which the advantage of a new drug over available therapy may not be a direct therapeutic advantage, but is a clinically important improvement from a patient and public health perspective. If granted, accelerated approval is usually contingent on the sponsor’s agreement to conduct, in a diligent manner, additional post-approval confirmatory studies to verify and describe the drug’s clinical benefit. If such confirmatory studies fail to confirm the drug’s clinical benefit or are not completed in a timely manner, the FDA may withdraw its approval of the drug on an expedited basis. In addition, the Food and Drug Omnibus Reform Act of 2022, among other things, provided the FDA with statutory authority to mitigate potential risks to patients from continued marketing of ineffective drugs previously granted accelerated approval and additional oversight over confirmatory trials. Under these provisions, the FDA may, among other things, require a sponsor of a product seeking accelerated approval to have a confirmatory trial underway prior to such approval being granted.

Prior to seeking approval for any ecDTx, Boundless Bio intends to seek feedback from the FDA and will otherwise evaluate its ability to seek and receive accelerated approval. There can be no assurance that after its evaluation of the feedback and other factors Boundless Bio will decide to pursue or submit an NDA for accelerated approval or obtain any other form of expedited development, review, or approval. Furthermore, if Boundless Bio decides to submit an application for accelerated approval for its ecDTx, there can be no assurance that such submission or application will be accepted or that any expedited development, review, or approval will be granted on a timely basis, or at all. The FDA could also require Boundless Bio to conduct further studies prior to considering its application or granting approval of any type. A failure to obtain accelerated approval or any other form of expedited development, review, or approval for its ecDTx would result in a longer time period to commercialization of such ecDTx, if any, could increase the cost of development of such ecDTx, and could harm its competitive position in the marketplace.

Disruptions at the FDA, the SEC, and other government agencies, including due to government shutdowns, other funding shortages, policy changes, leadership changes, layoffs or significant personnel turnover, or public health concerns, could impede development and potential marketing approval of Boundless Bio’s ecDTx and its ability to raise capital.

Over the last several years, the U.S. government has shut down several times and certain federal regulatory agencies, such as the FDA and SEC, furloughed or laid off employees and halted non-essential operations due to the failure of Congress to pass a new appropriations bill or continuing resolution to temporarily extend funding. Political polarization among lawmakers may lead to a higher frequency and longer duration of government shutdowns in the future. A federal government shutdown or other disruption to ordinary course operations could prevent or delay staff at federal agencies from performing key functions that may adversely affect Boundless Bio’s business, and the more prolonged the disruption, the greater risks it may pose to its business. In addition, considerable uncertainty exists regarding the current U.S. presidential administration’s initiatives and how these might impact federal government agencies, including the FDA, their implementation of laws, regulations, policies, and guidance, and their personnel. Alternatively, state governments may attempt to address or react to changes at the federal level with changes to their own regulatory frameworks in a manner that is adverse to Boundless Bio’s business or operations.

The ability of the FDA to review and approve new product applications or take action with respect to other regulatory matters can be affected by a variety of factors, including funding levels, ability to accept the payment

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of user fees, ability to hire and retain key personnel, and statutory, regulatory, and policy changes. Government funding of other government agencies that fund research and development activities is subject to the political process, which is inherently fluid and unpredictable. For example, the current U.S. presidential administration has issued certain policies and executive orders directed towards reducing, and subsequent reductions have occurred to, the employee headcount and costs associated with U.S. administrative agencies, including the FDA, and it remains unclear the degree to which these efforts may limit or otherwise adversely affect the FDA’s ability to conduct routine activities. Disruptions at the FDA may delay meetings and other communications with agency staff necessary to progress development of Boundless Bio’s ecDTx and may slow the time necessary for acceptance, review, and approval of applications to commence clinical studies or to market a new product in the U.S., which could also adversely affect its operating results and financial condition.

In addition, disruptions at the SEC could prevent or delay SEC staff from performing key functions, including, for example, granting acceleration requests for registration statements, declaring registration statements or amendments thereto effective and providing interpretive guidance or no-action letters. If a federal government shutdown halts non-essential SEC operations for an extended period, it may negatively impact Boundless Bio’s ability to raise additional capital through registered offerings of its securities. If a prolonged U.S. government shutdown or other event or condition occurs that prevents or significantly delays the FDA, SEC or other regulatory agencies from hiring and retaining personnel and conducting their regular activities, or if an agency is restructured or experiences significant reduction in funding, leadership changes, or employee turnover, it could significantly impact the ability of these agencies to timely review and process Boundless Bio’s regulatory submissions and may impede its access to additional capital needed to maintain or expand its operations or to complete important acquisitions or other transactions, which could have a material adverse effect on its business.

Risks Related to Boundless Bio’s Reliance on Third Parties

Boundless Bio relies on third parties to conduct Boundless Bio’s clinical trials and preclinical studies. If these third parties do not successfully carry out their contractual duties, comply with applicable regulatory requirements, or meet expected deadlines, Boundless Bio’s current or future ecDTx development programs and ability to seek or obtain regulatory approval for or commercialize its ecDTx may be delayed.

Boundless Bio is and will be dependent on third parties to conduct its clinical trials and preclinical studies for development of any ecDTx. Specifically, Boundless Bio has relied on, and will continue to rely on, medical institutions, clinical investigators, CROs, and consultants to conduct its preclinical studies and clinical trials in accordance with its clinical protocols and regulatory requirements. These CROs, investigators, and other third parties play a significant role in the conduct and timing of these trials and subsequent collection and analysis of data. While Boundless Bio has and will have agreements governing the activities of its third-party contractors, Boundless Bio has limited influence over their actual performance. Nevertheless, Boundless Bio is responsible for ensuring that each of Boundless Bio’s clinical trials is conducted in accordance with the applicable protocol and legal, regulatory, and scientific standards and requirements, and Boundless Bio’s reliance on its CROs and other third parties does not relieve Boundless Bio of regulatory responsibilities. In addition, Boundless Bio and its CROs are required to comply with Good Laboratory Practice (“GLP”) requirements for certain preclinical studies, as well as GCP requirements, which are regulations and guidelines enforced by the FDA and comparable foreign regulatory authorities for clinical trials of all of its ecDTx. Regulatory authorities enforce these GCPs through periodic inspections of trial sponsors, principal investigators, and trial sites. If Boundless Bio or any of its CROs or trial sites fail to comply with applicable GLP or GCP or other requirements, the clinical data generated in Boundless Bio’s preclinical studies or clinical trials may be deemed unreliable, and the FDA or comparable foreign regulatory authorities may require Boundless Bio to perform additional preclinical studies or clinical trials before approving Boundless Bio’s marketing applications, if ever. Further, Boundless Bio’s clinical trials must be conducted with products produced in accordance with cGMP regulations. Failure to comply with these regulations may require Boundless Bio to repeat clinical trials, which would delay the regulatory approval process.

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There is no guarantee that any of Boundless Bio’s CROs, investigators, or other third parties will devote adequate time and resources to such trials or studies or perform as contractually required. If any of these third parties fail to meet expected deadlines, adhere to Boundless Bio’s clinical protocols, or meet regulatory requirements, or otherwise perform in a substandard manner, Boundless Bio’s clinical trials may be extended, delayed, or terminated. In addition, many of the third parties with whom Boundless Bio contracts may also have relationships with other commercial entities, including its competitors, for whom they may also be conducting clinical trials or other development activities that could harm its competitive position.

Boundless Bio’s CROs have the right to terminate their agreements with Boundless Bio in the event of an uncured material breach and under other specified circumstances. If any of Boundless Bio’s relationships with these third parties terminate, Boundless Bio may not be able to enter into arrangements with alternative third parties on commercially reasonable terms, in a timely manner or at all. Switching or adding additional CROs, investigators, and other third parties involves additional cost and requires Boundless Bio’s management’s time and focus. In addition, there is a natural transition period when a new CRO commences work. As a result, delays occur, which can materially impact its ability to meet its desired clinical development timelines. Though Boundless Bio works to carefully manage its relationships with its CROs, investigators and other third parties, there can be no assurance that Boundless Bio will not encounter challenges or delays in the future or that these delays or challenges will not have a material adverse impact on its business, financial condition, and prospects.

If the Merger is not completed and Boundless Bio continues to develop any ecDTx, Boundless Bio expects to continue to rely on third parties for the manufacture of its ecDTx for clinical and preclinical development and expects to continue to do so for the foreseeable future. This reliance on third parties increases the risk that Boundless Bio will not have sufficient quantities of its ecDTx or products or such quantities at an acceptable cost, which could delay, prevent, or impair, its development or commercialization efforts.

Boundless Bio does not own or operate manufacturing facilities and has no plans to develop its own clinical or commercial-scale manufacturing capabilities. If Boundless Bio continues to develop any ecDTx, Boundless Bio expects to continue to rely on third parties, some of which operate outside of the U.S., for the manufacture of its ecDTx and related raw materials and to package, label, ship, store, and distribute its ecDTx for clinical and preclinical development, and Boundless Bio intends to rely on third parties for such services for its commercial products if any marketing approval is obtained. This reliance on third parties increases the risk that timely availability of clinical trial supplies of its ecDTx, and future products, if any, may be delayed, limited, or interrupted, or that their quality or cost is not satisfactory or acceptable. The facilities used by third-party manufacturers to manufacture its ecDTx must be approved for the manufacture of its ecDTx by the FDA and any comparable foreign regulatory authority pursuant to inspections that will be conducted after Boundless Bio submits an NDA to the FDA or any comparable submission to a foreign regulatory authority. Boundless Bio does not control the manufacturing process of, and is completely dependent on, third-party manufacturers for compliance with cGMP requirements for manufacture of products. If these third-party manufacturers cannot successfully manufacture material that conforms to Boundless Bio’s specifications and the strict regulatory requirements of the FDA or any comparable foreign regulatory authority, they will not be able to secure and/or maintain regulatory approval for their manufacturing facilities. In addition, Boundless Bio has no control over the ability of third-party manufacturers to maintain adequate quality control, quality assurance, and qualified personnel. If the FDA or any comparable foreign regulatory authority does not approve these facilities for the manufacture of its ecDTx or if it withdraws any such approval in the future, Boundless Bio may need to find alternative manufacturing facilities, which would significantly impact its ability to develop, obtain regulatory approval for, or market its ecDTx, if approved. Boundless Bio’s failure, or the failure of Boundless Bio’s third-party manufacturers, to comply with applicable regulations could result in sanctions being imposed on Boundless Bio, including clinical holds, fines, injunctions, civil penalties, delays, suspension or withdrawal of approvals, seizures or recalls of ecDTx or products, operating restrictions, and criminal prosecutions, any of which could significantly and adversely affect supplies of its ecDTx.

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Boundless Bio’s or a third party’s failure to execute on its manufacturing requirements on commercially reasonable terms, in a timely manner and in compliance with cGMP or other regulatory requirements could adversely affect Boundless Bio’s business in a number of ways, including:

We have relied and may in the future rely on foreign CMOs. Such foreign CMOs may be subject to U.S. legislation, sanctions, trade restrictions, and other foreign regulatory requirements which could increase the cost or reduce the supply of material available to Boundless Bio, delay the procurement or supply of such material, or have an adverse effect on Boundless Bio’s ability to secure significant commitments from governments to purchase its potential therapies. For example, in January 2024, there was congressional activity, including the introduction of the BIOSECURE Act (“H.R. 7085”) in the House of Representatives and a substantially similar Senate bill (“S.3558”). A version of the BIOSECURE Act was passed by the U.S. House of Representatives in September 2024 (“H.R. 8333”), however, the Senate did not approve that legislation. In October 2025, both the U.S. House of Representatives and Senate passed their respective versions of the National Defense Authorization Act of 2026 (“NDAA”), each including an amendment often referred to as “BIOSECURE 2.0.” BIOSECURE 2.0 was reconciled in conference and signed into law on December 18, 2025. BIOSECURE 2.0 establishes federal government contracting, grant, and loan restrictions similar in effect to previously introduced bills. BIOSECURE 2.0 implements a process-based designation system through which biotechnology companies “of concern” are identified based on whether such companies fall within statutorily defined categories, including entities identified on the Department of Defense’s Section 1260H list of “Chinese military companies” and other entities that are subject to the administrative governance structure, direction, control, or jurisdiction of a foreign adversary’s government which pose national security risks based on specified criteria. The prohibitions of BIOSECURE 2.0 will become effective approximately three years after the enactment of BIOSECURE 2.0 (i.e., December 2028). BIOSECURE 2.0 has the potential to severely restrict the ability of U.S. biopharmaceutical companies like Boundless Bio to purchase products or services from, or otherwise collaborate with, certain Chinese biotechnology companies “of concern” without losing the ability to contract with, or otherwise receive funding from, the U.S. government. It is possible some of Boundless Bio’s Chinese CMOs and other Chinese vendors, could be impacted by this legislation.

In addition, Boundless Bio does not have any long-term commitments or supply agreements with its third-party manufacturers. Boundless Bio may be unable to establish any long-term supply agreements with third-party manufacturers or to do so on acceptable terms or at all, which increases the risk of failing to timely obtain sufficient quantities of its ecDTx or such quantities at an acceptable cost. Even if Boundless Bio is able to establish agreements with third-party manufacturers, reliance on third-party manufacturers entails additional risks, including:

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Boundless Bio’s ecDTx and any products that Boundless Bio may develop may compete with other product candidates and products for access to manufacturing facilities.

Any performance failure on the part of Boundless Bio’s existing or future manufacturers could delay clinical development or regulatory approval, and any related remedial measures may be costly or time consuming to implement. Boundless Bio does not currently have arrangements in place for redundant supply or a second source for all required raw materials used in the manufacture of Boundless Bio’s ecDTx. If Boundless Bio’s existing or future third-party manufacturers cannot perform as agreed, Boundless Bio may be required to replace such manufacturers if Boundless Bio continues to develop any ecDTx and Boundless Bio may be unable to replace them on a timely basis or at all.

In addition, Boundless Bio’s current and anticipated future dependence upon others for the manufacture of its ecDTx or products may adversely affect its future profit margins and Boundless Bio’s ability to commercialize any products that receive regulatory approval on a timely and competitive basis.

Boundless Bio’s reliance on third parties requires Boundless Bio to share its trade secrets, which increases the possibility that a competitor or other third party will discover them or that its trade secrets will be misappropriated or disclosed.

Because Boundless Bio will rely on third parties to manufacture its ecDTx and to perform quality testing if Boundless Bio continues to develop an ecDTx, Boundless Bio must, at times, share Boundless Bio’s proprietary technology and confidential information, including trade secrets, with them. Boundless Bio seeks to protect Boundless Bio’s proprietary technology, in part, by entering into confidentiality agreements, and, if applicable, material transfer agreements, collaborative research agreements, consulting agreements, or other similar agreements with Boundless Bio’s collaborators, advisors, employees, and consultants prior to beginning research or disclosing proprietary information. These agreements typically limit the rights of third parties to use or disclose its confidential information. Despite the contractual provisions employed when working with third parties, the need to share trade secrets and other confidential information increases the risk that such trade secrets become known by Boundless Bio’s competitors or other third parties, are intentionally or inadvertently incorporated into the technology of others, or are disclosed or used in violation of these agreements. Given that Boundless Bio’s proprietary position is based, in part, on its know-how and trade secrets and despite its efforts to protect its trade secrets, a competitor’s or other third party’s discovery of Boundless Bio’s proprietary technology and confidential information or other unauthorized use or disclosure of such technology or information would impair Boundless Bio’s competitive position and may have a material adverse effect on Boundless Bio’s business, financial condition, results of operations, and prospects.

If the Merger is not completed, Boundless Bio may seek to enter into collaborations, licenses, and other similar arrangements and may not be successful in doing so, and even if Boundless Bio is successful, it may relinquish valuable rights and may not realize the benefits of such relationships.

If the Merger is not completed, Boundless Bio may seek to enter into collaborations, joint ventures, licenses, and other similar arrangements for the development or commercialization of its ecDTx, if approved, due to

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capital costs required to develop or commercialize the ecDTx or manufacturing constraints. Boundless Bio may not be successful in its efforts to establish or maintain such collaborations for its ecDTx because its research and development pipeline may be insufficient, its ecDTx may be deemed to be at too early of a stage of development for collaborative effort, or third parties may not view its ecDTx as having the requisite potential to demonstrate safety and efficacy or significant commercial opportunity. In addition, Boundless Bio faces significant competition in seeking appropriate strategic partners, and the negotiation process can be time-consuming and complex. Even if Boundless Bio is successful in its efforts to establish such collaborations, the terms that Boundless Bio agrees upon may not be favorable. For example, Boundless Bio may need to relinquish valuable rights to its future revenue streams, research programs, intellectual property, ecDTx or a diagnostic assay, or grant licenses on terms that may not be favorable as part of any such arrangement, and such arrangements may restrict Boundless Bio from entering into additional agreements with other potential collaborators. In addition, if Boundless Bio enter into such collaborations, it will have limited control over the amount and timing of resources that its collaborators will dedicate to the development or commercialization of its ecDTx. Boundless Bio’s ability to generate revenue from these arrangements will depend on any future collaborators’ abilities to successfully perform the functions assigned to them in these arrangements. Boundless Bio cannot be certain that, following a collaboration, license, or strategic transaction, Boundless Bio will achieve an economic benefit that justifies such transaction, and such transaction may not yield additional development or ecDTx for its pipeline. Furthermore, Boundless Bio may not be able to maintain such collaborations if, for example, the development or approval of an ecDTx is delayed, the safety of an ecDTx is questioned, or the sales of an approved ecDTx are unsatisfactory.

In addition, any potential future collaborations may be terminable by Boundless Bio’s strategic partners, and Boundless Bio may not be able to adequately protect its rights under these agreements. Furthermore, strategic partners may negotiate for certain rights to control decisions regarding the development and commercialization of its ecDTx, if approved, and may not conduct those activities in the same manner as Boundless Bio does. Any termination of collaborations Boundless Bio enters into in the future, or any delay in entering into collaborations related to its ecDTx, could delay the development and commercialization of its ecDTx, if approved, and reduce its competitiveness if it reaches the market, which could have a material adverse effect on its business, financial condition, results of operations, and prospects.

Risks Related to Commercialization of Boundless Bio’s ecDTx

Even if Boundless Bio receives regulatory approval for any ecDTx, Boundless Bio will be subject to ongoing regulatory obligations and continued regulatory review, which may result in significant additional expense.

Any regulatory approvals that Boundless Bio may receive for its ecDTx will require the submission of reports to regulatory authorities, subject Boundless Bio to surveillance to monitor the safety and efficacy of the product, may contain significant limitations related to use restrictions for specified age groups, warnings, precautions, or contraindications, and may include burdensome post-approval study or risk management requirements. For example, the FDA may require a REMS as a condition of approval of Boundless Bio’s ecDTx, which could include requirements for a medication guide, physician communication plans, or additional elements to ensure safe use, such as restricted distribution methods, patient registries, and other risk minimization tools.

In addition, if the FDA or a comparable foreign regulatory authority approves Boundless Bio’s ecDTx, the manufacturing processes, labeling, packaging, distribution, adverse event reporting, storage, advertising, promotion, import, export, and recordkeeping for its products will be subject to extensive and ongoing regulatory requirements. These requirements include submissions of safety and other post-marketing information and reports, registration, as well as continued compliance with cGMPs and GCP requirements for any clinical trials that Boundless Bio conducts post-approval. Manufacturers of approved products and their facilities are subject to continual review and periodic, unannounced inspections by the FDA and other regulatory authorities for compliance with cGMP regulations and standards. Failure to comply with regulatory requirements or later discovery of previously unknown problems with Boundless Bio’s products, including adverse events of

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unanticipated severity or frequency, or with Boundless Bio’s third-party manufacturers or manufacturing processes, may result in, among other things:

The occurrence of any event or penalty described above may inhibit Boundless Bio’s ability to commercialize its ecDTx and generate revenue and could require Boundless Bio to expend significant time and resources in response and could generate negative publicity.

The FDA’s and other regulatory authorities’ policies may change, and additional government regulations may be promulgated that could prevent, limit, or delay marketing authorization of any ecDTx. Boundless Bio also cannot predict the likelihood, nature, or extent of government regulation that may arise from future legislation or administrative action, either in the United States or abroad. If Boundless Bio is slow or unable to adapt to changes in existing requirements or the adoption of new requirements or policies, or if Boundless Bio is not able to maintain regulatory compliance, Boundless Bio may be subject to enforcement action and Boundless Bio may not achieve or sustain profitability.

The FDA and other regulatory agencies actively enforce the laws and regulations prohibiting the promotion of off-label uses.

The FDA and other regulatory agencies strictly regulate the promotional claims that may be made about prescription products, such as Boundless Bio’s ecDTx, if approved. In particular, a product may not be promoted for uses that are not approved by the FDA or such other regulatory agencies as reflected in the product’s approved labeling. If Boundless Bio receives regulatory approval for an ecDTx, physicians may nevertheless prescribe it to their patients in a manner that is inconsistent with the approved label. If Boundless Bio is found to have promoted such off-label uses, Boundless Bio may become subject to significant liability. The U.S. federal government has levied large civil and criminal fines against companies for alleged improper promotion of off-label use and has enjoined several companies from engaging in off-label promotion. The government has also required companies to enter into consent decrees or imposed permanent injunctions under which specified promotional conduct is changed or curtailed. If Boundless Bio cannot successfully manage the promotion of its ecDTx, if approved, Boundless Bio could become subject to significant liability, which would materially adversely affect its business and financial condition.

The commercial success of any Boundless Bio ecDTx will depend upon the degree of market acceptance of such ecDTx by physicians, patients, healthcare payors, and others in the medical community.

Any Boundless Bio ecDTx may not be commercially successful. Even if any Boundless Bio ecDTx receives regulatory approval, it may not gain market acceptance among physicians, patients, healthcare payors, or the

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medical community. The commercial success of Boundless Bio’s ecDTx will depend significantly on the broad adoption and use of the resulting product by these individuals and organizations for approved indications. The degree of market acceptance of Boundless Bio’s products will depend on a number of factors, including:

If any ecDTx is approved but does not achieve an adequate level of acceptance by physicians, hospitals, healthcare payors, or patients, Boundless Bio may not generate sufficient revenue from that product and may not become or remain profitable. Boundless Bio’s efforts to educate the medical community and third-party payors regarding the benefits of Boundless Bio’s products may require significant resources and may never be successful.

The successful commercialization of Boundless Bio’s ecDTx, if approved, will depend in part on the extent to which governmental authorities and health insurers establish coverage, adequate reimbursement levels, and favorable pricing policies. Failure to obtain or maintain coverage and adequate reimbursement for Boundless Bio’s ecDTx could limit its ability to market those products and decrease Boundless Bio’s ability to generate revenue.

The availability of coverage and the adequacy of reimbursement by governmental healthcare programs such as Medicare and Medicaid, private health insurers, and other third-party payors are essential for most patients to be able to afford prescription medications such as Boundless Bio’s ecDTx, if approved. If the Merger is not completed and Boundless Bio continues to develop any ecDTx, Boundless Bio’s ability to achieve coverage and adequate levels of reimbursement for its ecDTx by third-party payors will have a material effect on its ability to successfully commercialize its ecDTx. Accordingly, Boundless Bio will need to successfully implement a coverage and reimbursement strategy for any approved ecDTx. Even if Boundless Bio obtains coverage for a given ecDTx by a third-party payor, the resulting reimbursement payment rates may not be adequate or may require co-payments that patients find unacceptably high. Reimbursement for drugs by government healthcare programs may be reduced by mandatory discounts or rebates required by such programs. Certain government healthcare programs impose ceiling prices on products of participating manufacturers.

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Third-party payors increasingly are challenging prices charged for biopharmaceutical products and services, and many third-party payors may refuse to provide coverage and reimbursement for particular drugs when an equivalent generic drug or a less expensive therapy is available. It is possible that a third-party payor may consider Boundless Bio’s ecDTx as substitutable and offer to reimburse patients only for the less expensive product. Even if Boundless Bio is successful in demonstrating improved efficacy or improved convenience of administration with its ecDTx, pricing of existing drugs may limit the amount Boundless Bio will be able to charge for its ecDTx. These payors may deny or revoke the reimbursement status of a given product or establish prices for new or existing marketed products at levels that are not adequate to enable Boundless Bio to realize an appropriate return on its investment in ecDTx development. If reimbursement is not available or is available only at inadequate levels, Boundless Bio may not be able to successfully commercialize its ecDTx and may not be able to obtain a satisfactory financial return on ecDTx that Boundless Bio may develop. In addition, in the event that Boundless Bio develops companion diagnostic tests for use with its ecDTx, once approved, such diagnostic tests will require coverage and reimbursement separate and apart from the coverage and reimbursement for their companion pharmaceutical product. Similar challenges to obtaining coverage and reimbursement applicable to pharmaceutical products will apply to companion diagnostics tests.

There is significant uncertainty related to third-party payor coverage and reimbursement of newly approved products. In the United States, third-party payors, including private and governmental payors, such as the Medicare and Medicaid, play an important role in determining the extent to which new drugs will be covered. Some third-party payors may require pre-approval of coverage for new or innovative devices or drug therapies before they will reimburse healthcare providers who use such therapies. It is difficult to predict at this time what third-party payors will decide with respect to the coverage and reimbursement for Boundless Bio’s products.

Obtaining and maintaining reimbursement status is time-consuming, costly, and uncertain. The Medicare and Medicaid programs increasingly are used as models for how private payors and other governmental payors develop their coverage and reimbursement policies for drugs. However, no uniform policy for coverage and reimbursement for products exists among third-party payors in the United States. Therefore, coverage and reimbursement for products can differ significantly from payor to payor. As a result, the coverage determination process is often time consuming and costly and may require Boundless Bio to provide scientific and clinical support for the use of its ecDTx to each payor separately, with no assurance that coverage and adequate reimbursement will be applied consistently or obtained in the first instance. Reimbursement practices are also subject to rules and regulations that may change frequently, and, in some cases, at short notice.

Outside the United States, international operations are generally subject to extensive governmental price controls and other market regulations, and Boundless Bio believes the increasing emphasis on cost-containment initiatives in Europe and other countries has and will continue to put pressure on the pricing and usage of its ecDTx, if approved in these jurisdictions. In many countries, the prices of medical products are subject to varying price control mechanisms as part of national health systems. Other countries allow companies to fix their own prices for medical products but monitor and control company profits. Additional foreign price controls or other changes in pricing regulation could restrict the amount that Boundless Bio is able to charge for its ecDTx. Accordingly, in markets outside the United States, the reimbursement for Boundless Bio’s products may be reduced compared with the United States and may be insufficient to generate commercially reasonable revenue and profits.

Moreover, increasing efforts by governmental and third-party payors in the United States and abroad to cap or reduce healthcare costs may cause such organizations to limit both coverage and the level of reimbursement for newly approved products and, as a result, they may not cover or provide adequate payment for Boundless Bio’s ecDTx. Boundless Bio expects to experience pricing pressures in connection with the sale of its ecDTx due to the trend toward managed healthcare, the increasing influence of health maintenance organizations and additional legislative changes. There is increasing downward pressure on healthcare costs in general, and prescription drugs, surgical procedures, and other treatments in particular. As a result, increasingly high barriers are being erected to the entry of new products. See the section titled “Risk Factors — Risks Related to Boundless Bio — Risks Related to Boundless Bio’s Business Operations and Industry — Current and future healthcare reform legislation or regulation may increase the difficulty and cost for Boundless Bio to obtain coverage for and commercialize its ecDTx and may adversely affect the prices it may set” for additional related information.

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Boundless Bio faces significant competition from entities that have developed or may develop product candidates for cancer, including companies developing novel treatments and technology platforms. If Boundless Bio’s competitors develop and commercialize their product candidates more rapidly than Boundless Bio does, or their technologies or their product candidates are more effective, safer, or less expensive than Boundless Bio’s ecDTx, Boundless Bio’s business and its ability to develop and successfully commercialize ecDTx may be adversely affected.

The biopharmaceutical industry is characterized by rapid advancing technologies, intense competition, and a strong emphasis on proprietary and novel products and product candidates. Boundless Bio’s competitors have developed, are developing, or may develop products or product candidates competitive with Boundless Bio’s ecDTx. If the Merger is not completed and Boundless Bio continues to develop any ecDTx, any ecDTx that Boundless Bio successfully develops and commercializes will compete with existing therapies and new therapies that may become available in the future. Boundless Bio believes that a significant number of products are currently under development, and may become commercially available in the future, for the treatment of indications for which Boundless Bio may attempt to develop ecDTx. In particular, there is intense competition in the oncology field. Boundless Bio’s competitors include larger and better-funded pharmaceutical, biopharmaceutical, biotechnological, and therapeutics companies. Moreover, Boundless Bio may also compete with universities and other research institutions that may be active in oncology research and could be in direct competition with Boundless Bio. Boundless Bio also competes with these organizations to recruit management, scientists, and clinical development personnel, and Boundless Bio’s inability to compete successfully could negatively affect its level of expertise and its ability to execute its business plan. Boundless Bio will also face competition in establishing clinical trial sites, enrolling patients for clinical trials, and identifying and in-licensing intellectual property related to new ecDTx, as well as entering into collaborations, joint ventures, license agreements, and other similar arrangements. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

If Boundless Bio’s ecDTx is approved, it will compete with surgery, radiation, and drug therapy, including chemotherapy, hormone therapy, biologic therapy, such as monoclonal and bispecific antibodies, antibody-drug conjugates, radiopharmaceuticals, immunotherapy, cell-based therapy, and targeted therapy, or a combination of any such methods, either approved or under development, that are intended to treat the same indications that Boundless Bio is targeting or may target, including through approaches that may prove to be more effective, have fewer side effects, be less costly to manufacture, be more convenient to administer, or have other advantages over Boundless Bio’s ecDTx. There are numerous companies developing precision oncology medicines with which Boundless Bio may compete. In addition to competing with other therapies targeting similar indications, there are numerous other companies and academic institutions focused on similar targets as its ecDTx and/or different scientific approaches to treating the same indications. Boundless Bio faces competition from such companies in seeking any future potential collaborations to partner its ecDTx, as well as potentially competing commercially for any approved products.

Many of Boundless Bio’s competitors have significantly greater financial, technical, manufacturing, marketing, sales, and supply resources or experience than Boundless Bio does. If Boundless Bio successfully obtains approval for any ecDTx, Boundless Bio will face competition based on many different factors, including the safety and effectiveness of its products, the ease with which its products can be administered, and the extent to which patients accept relatively new routes of administration, the timing and scope of regulatory approvals for these products, the availability and cost of manufacturing, marketing, and sales capabilities, price, reimbursement coverage, and patent position. Competing products could present superior treatment alternatives, including by being more effective, safer, more convenient, less expensive, or marketed and sold more effectively than any products Boundless Bio may develop. Competitive products may make any ecDTx Boundless Bio develops obsolete or noncompetitive before Boundless Bio recovers the expense of developing and commercializing it. If Boundless Bio is unable to compete effectively, its opportunity to generate revenue from the sale of any ecDTx Boundless Bio may develop, if approved, could be adversely affected.

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The market opportunities for Boundless Bio’s ecDTx may be limited to patients who are ineligible for or have failed prior treatments and may be small or different from Boundless Bio’s estimates.

Cancer therapies are defined by lines of therapy as well as by treatment-naïve or previously-treated status. Often the initial approval for a new therapy is in later lines and subsequent approval in an earlier line may not be feasible. When cancer is detected early enough, first line therapy is sometimes adequate to cure the cancer or prolong life without a cure. Whenever first line therapy, including surgery, radiation therapy, targeted therapy, immunotherapy, chemotherapy, hormone therapy, or a combination of these, proves unsuccessful, second line therapy may be administered. Second line therapies often consist of additional chemotherapy, radiation, antibody drugs, tumor targeted small molecules, or a combination of these. Third line therapies can include antibody and small molecule targeted therapies, more invasive forms of surgery, and new technologies. In markets with approved therapies, there is no guarantee that Boundless Bio’s ecDTx, even if approved, would be approved for second line or first line therapy. This could limit Boundless Bio’s potential market opportunity. In addition, Boundless Bio may have to conduct additional clinical trials prior to gaining approval for second line or first line therapy.

Boundless Bio’s projections of both the number of people who have the cancers Boundless Bio is targeting, as well as the subset of people with these cancers in a position to receive later stage therapy and who have the potential to benefit from treatment with its ecDTx, are based on Boundless Bio’s beliefs and estimates. These estimates have been derived from a variety of sources, including scientific literature, publicly available clinical molecular reports, patient foundations, or market research, and may prove to be incorrect. Further, new trials or information may change the estimated incidence or prevalence of these cancers. Further, specific to Boundless Bio’s biomarker-driven strategy, data analytics, and information from databases that Boundless Bio relies on for identifying or validating some of its biomarker-target relationships may not accurately reflect potential patient populations or may be based on incorrect methodology. As ecDNA in oncogene amplified cancers is a new and novel approach, this heightens the risk that Boundless Bio’s estimates of the eligible patient population may not be accurate. The number of patients in the United States and other major markets and elsewhere may turn out to be lower than expected, patients may not be otherwise amenable to treatment with Boundless Bio’s products, or new patients may become increasingly difficult to identify or gain access to, all of which would adversely affect Boundless Bio’s results of operations and Boundless Bio’s business. Further, even if Boundless Bio obtains significant market share for its ecDTx, because some of Boundless Bio’s potential target populations are very small, it may never achieve profitability despite obtaining such significant market share.

Boundless Bio currently has no marketing and sales organization and have no experience as a company in commercializing products, and Boundless Bio may need to invest significant resources to develop these capabilities. If Boundless Bio is unable to establish marketing and sales capabilities or enter into agreements with third parties to market and sell its products, Boundless Bio may not be able to generate product revenue.

Boundless Bio has no internal sales, marketing, or distribution capabilities, nor has Boundless Bio ever commercialized a product. If the Merger is not completed and Boundless Bio’s ecDTx ultimately receives regulatory approval, Boundless Bio must build a marketing and sales organization with technical expertise and supporting distribution capabilities to commercialize each such product in major markets, which will be expensive and time consuming, or collaborate with third parties that have direct sales forces and established distribution systems, either to augment Boundless Bio’s own sales force and distribution systems or in lieu of Boundless Bio’s own sales force and distribution systems. Boundless Bio has no prior experience as a company with the marketing, sale, or distribution of biopharmaceutical products, and there are significant risks involved in the building and managing of a sales organization, including Boundless Bio’s ability to hire, retain, and incentivize qualified individuals, generate sufficient sales leads, provide adequate training to sales and marketing personnel, and effectively manage a geographically dispersed sales and marketing team. Any failure or delay in the development of Boundless Bio’s internal sales, marketing, and distribution capabilities would adversely impact the commercialization of these products. Boundless Bio may not be able to enter into collaborations or hire consultants or external service providers to assist Boundless Bio in sales, marketing, and distribution functions on acceptable financial terms, or at all. In addition, Boundless Bio’s ecDTx revenue and its profitability, if any, may be lower if Boundless Bio relies on third parties for these functions than if it were to

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market, sell, and distribute any ecDTx that Boundless Bio develops itself. Boundless Bio will likely have little control over such third parties, and any of them may fail to devote the necessary resources and attention to sell and market Boundless Bio’s ecDTx effectively. If Boundless Bio is not successful in commercializing its ecDTx, either on Boundless Bio’s own or through arrangements with one or more third parties, Boundless Bio may not be able to generate any future ecDTx revenue and Boundless Bio would incur significant additional losses.

Boundless Bio’s future growth may depend, in part, on Boundless Bio’s ability to operate in foreign markets, where Boundless Bio would be subject to additional regulatory burdens and other risks and uncertainties.

Boundless Bio’s future growth may depend, in part, on Boundless Bio’s ability to develop and commercialize its ecDTx in foreign markets. Boundless Bio is not permitted to market or promote Boundless Bio’s ecDTx before Boundless Bio receives regulatory approval from applicable regulatory authorities in foreign markets, and Boundless Bio may never receive such regulatory approvals for its ecDTx. To obtain separate regulatory approval in many other countries Boundless Bio must comply with numerous and varying regulatory requirements regarding safety and efficacy and governing, among other things, clinical trials, commercial sales, pricing, and distribution of Boundless Bio’s ecDTx. Approval procedures may be more onerous than those in the United States and may require that Boundless Bio conducts additional preclinical studies or clinical trials. If Boundless Bio obtains regulatory approval of its ecDTx and ultimately commercialize its ecDTx in foreign markets, Boundless Bio would be subject to additional risks and uncertainties, including:

Risks Related to Boundless Bio’s Business Operations and Industry

Boundless Bio’s operating results may fluctuate significantly, which makes its future operating results difficult to predict and could cause its operating results to fall below expectations or any guidance Boundless Bio may provide.

Boundless Bio’s quarterly and annual operating results may fluctuate significantly, which makes it difficult for Boundless Bio to predict its future operating results. These fluctuations may occur due to a variety of factors, many of which are outside of its control, including, but not limited to:

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The cumulative effects of these factors could result in large fluctuations and unpredictability in Boundless Bio’s quarterly and annual operating results. As a result, comparing Boundless Bio’s operating results on a period-to-period basis may not be meaningful. Investors should not rely on Boundless Bio’s past results as an indication of Boundless Bio’s future performance.

This variability and unpredictability could also result in Boundless Bio’s failing to meet the expectations of industry or financial analysts or investors for any period. If Boundless Bio’s revenue or operating results fall below the expectations of analysts or investors or below any forecasts Boundless Bio may provide to the market, or if the forecasts Boundless Bio provides to the market are below the expectations of analysts or investors, the price of Boundless Bio Common Stock could decline substantially. Such a stock price decline could occur even when Boundless Bio has met any previously publicly stated revenue or earnings guidance Boundless Bio may provide.

Boundless Bio has a relatively small number of employees which may constrain its ability to accomplish its business objectives. If the Merger is not completed, Boundless Bio’s long-term success is dependent on its ability to retain and attract highly qualified management and other clinical and scientific personnel.

As of July 15, 2026, Boundless Bio had 15 employees, all of whom were full-time employees. Due to Boundless Bio’s relatively small workforce, Boundless Bio may experience constraints that impede the achievement of its business objectives. Further, if multiple employees were to become unable to work for a prolonged period, or if they were to resign at roughly the same time, Boundless Bio’s ability to effectively manage and operate its business could become significantly impaired.

If the Merger is not completed, Boundless Bio’s long-term success depends in part on its ability to attract, recruit, retain, manage, and motivate highly qualified management, clinical, and scientific personnel, and Boundless Bio faces significant competition for experienced personnel. Boundless Bio is highly dependent upon its senior management and other members of Boundless Bio’s management team. The loss of services of any of these individuals could delay or prevent the successful development of Boundless Bio’s product pipeline, initiation or completion of any clinical trials and preclinical studies, regulatory approvals, or the commercialization of its ecDTx. Although Boundless Bio has executed employment agreements or offer letters

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with each member of its senior management team, these agreements are terminable at will with or without notice and, therefore, Boundless Bio may not be able to retain their services as expected. For example, in connection with the Merger, the employment of Boundless Bio’s President and Chief Executive Officer terminated in July 2026 and the employment of Boundless Bio’s Chief Business Officer previously terminated in January 2025. Boundless Bio does not currently maintain “key person” life insurance on the lives of its executives or any of its employees. This lack of insurance means that Boundless Bio may not have adequate compensation for the loss of the services of these individuals.

In addition, employment candidates and existing employees often consider the value of the stock awards they receive in connection with their employment. If the perceived benefits of Boundless Bio’s stock awards decline, either due to the trading price of its stock or for other reasons, it may harm Boundless Bio’s ability to recruit and retain highly skilled employees. Boundless Bio’s ability to retain highly skilled employees may be negatively impacted by any significant appreciation or depreciation in its stock price relative to the exercise price of outstanding stock options.

In the future, if the Merger is not completed and Boundless Bio continues to develop any ecDTx, Boundless Bio will need to expand and effectively manage its managerial, operational, financial, and other resources in order to successfully pursue any clinical development and commercialization efforts. Boundless Bio may not be successful in maintaining its unique company culture and continuing to attract or retain qualified management, clinical, and scientific personnel in the future due to the intense competition for qualified personnel among biopharmaceutical, biotechnology, and other businesses. If Boundless Bio is not able to attract, integrate, retain, and motivate necessary personnel to accomplish its business objectives, Boundless Bio may experience constraints that will significantly impede the achievement of its development objectives, its ability to raise additional capital, and its ability to implement its business strategy.

Boundless Bio may encounter difficulties in managing its growth and expanding its operations successfully.

If Boundless Bio continues to develop an ecDTx, Boundless Bio will need to expand its financial, development, regulatory, manufacturing, information technology, marketing, and sales capabilities or contract with third parties to provide these capabilities for Boundless Bio. If Boundless Bio’s operations expand, Boundless Bio expects that it will need to manage additional relationships with various strategic partners, suppliers, and other third parties, and it may not be successful in doing so. Boundless Bio’s future financial performance and its ability to develop and commercialize its ecDTx and to compete effectively will depend, in part, on its ability to manage any future growth effectively.

Boundless Bio is subject to various U.S. federal, state, and foreign healthcare laws and regulations, which could increase compliance costs, and Boundless Bio’s failure to comply with these laws and regulations could harm its reputation, subject Boundless Bio to significant fines and liability, or otherwise adversely affect its business.

Boundless Bio’s business operations and current and future arrangements with investigators, healthcare professionals, consultants, third-party payors, patient organizations, and customers expose Boundless Bio to broadly applicable foreign, federal, and state fraud and abuse and other healthcare laws and regulations. These laws may constrain the business or financial arrangements and relationships through which Boundless Bio conducts its operations, including how Boundless Bio researches, markets, sells, and distributes any products for which Boundless Bio obtains regulatory approval. Such laws include:

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Efforts to ensure that Boundless Bio’s current and future business arrangements with third parties will comply with applicable healthcare and privacy laws and regulations will involve ongoing substantial costs. It is possible that governmental authorities will conclude that Boundless Bio’s business practices, including certain consulting agreements and advisory board agreements Boundless Bio has entered into with physicians who are paid, in part, in the form of stock or stock options, may not comply with current or future statutes, regulations or case law involving applicable fraud and abuse or other healthcare laws and regulations. Due to the breadth of these laws, the narrowness of statutory exceptions and regulatory safe harbors available, and the range of interpretations to which they are subject, it is possible that some of Boundless Bio’s current or future practices might be challenged under one or more of these laws. If Boundless Bio’s operations are found to be in violation of any of these laws or any other governmental regulations that may apply to Boundless Bio, Boundless Bio may be subject to significant penalties, including civil, criminal, and administrative penalties, damages, fines, disgorgement, imprisonment, exclusion from participation in government-funded healthcare programs, such as Medicare and Medicaid, integrity oversight and reporting obligations, contractual damages, reputational harm, diminished profits and future earnings, and the curtailment or restructuring of Boundless Bio’s operations. Defending against any such actions can be costly and time-consuming and may require significant financial and personnel resources. Therefore, even if Boundless Bio is successful in defending against any such actions that may be brought against Boundless Bio, its business may be impaired. Further, if any of the physicians or other healthcare providers or entities with whom Boundless Bio expects to do business are found not to be in compliance with applicable laws or regulations, they may be subject to significant criminal, civil, or administrative sanctions, including exclusions from government-funded healthcare programs.

Current and future healthcare reform legislation or regulation may increase the difficulty and cost for Boundless Bio to obtain coverage for and commercialize any ecDTx and may adversely affect the prices Boundless Bio may set.

In the United States and some foreign jurisdictions, there have been, and Boundless Bio expects there will continue to be, a number of legislative and regulatory changes to the healthcare system, including cost-containment measures, that may reduce or limit coverage and reimbursement for newly approved drugs and affect Boundless Bio’s ability to profitably sell any ecDTx for which Boundless Bio obtains regulatory approval. In particular, there have been and continue to be a number of initiatives at the U.S. federal and state levels that seek to reduce healthcare costs and improve the quality of healthcare.

For example, in March 2010, the Affordable Care Act (“ACA”) was enacted in the United States and substantially changed the way healthcare is financed by both the government and private insurers. The ACA contains provisions that may reduce the profitability of drug products. Among other things, the ACA established an annual, nondeductible fee on any entity that manufactures or imports specified branded prescription drugs and biologic agents; extended manufacturers’ Medicaid rebate liability to covered outpatient drugs dispensed to individuals who are enrolled in Medicaid managed care organizations; expanded eligibility criteria for Medicaid programs; expanded the entities eligible for discounts under the 340B drug pricing program; and increased the statutory minimum rebates a manufacturer must pay under the Medicaid Drug Rebate Program. Since its enactment, there have been executive, judicial, and Congressional challenges to certain aspects of the ACA. In June 2021, the U.S. Supreme Court dismissed the most recent judicial challenge to the ACA brought by several states without specifically ruling on the constitutionality of the ACA. The current U.S. presidential administration has made several changes to how the ACA is implemented. For example, in January 2025,

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President Trump issued Executive Order 14148, which revoked Executive Order 14009 issued by President Biden in January 2021, that had initiated a special enrollment period for purposes of obtaining health insurance coverage through the ACA marketplace. It is possible that the ACA will be subject to further judicial or Congressional challenges in the future. It is unclear what healthcare reform measures will be implemented by the current presidential administration going forward, but further changes are anticipated.

In addition, other legislative changes have been proposed and adopted since the ACA was enacted. In July 2025, the annual reconciliation bill, the “One Big Beautiful Bill Act” (“OBBBA”), was signed into law which is expected to reduce Medicaid spending and enrollment by shortening the open enrollment period, disqualifying Deferred Action for Childhood Arrivals (“DACA”) recipients, implementing work requirements for some beneficiaries, capping state-directed payments, reducing federal funding, and limiting provider taxes used to fund the program. OBBBA also narrows access to ACA marketplace exchange enrollment and declined to extend the ACA’s enhanced advanced premium tax credits, which expired in 2025, and these changes, among other provisions in the law, are anticipated to reduce the number of Americans with health insurance. Additionally, under the sequestration required by the Budget Control Act of 2011, beginning April 1, 2013, Medicare payments to providers were reduced, which will remain in effect through 2032 unless additional Congressional action is taken. Enacted in January 2013, the American Taxpayer Relief Act of 2012, among other things, reduced Medicare payments to several providers, including hospitals, and increased the statute of limitations period for the government to recover overpayments to providers from three to five years. Further, enacted in March 2021, the American Rescue Plan Act of 2021 eliminated the statutory Medicaid drug rebate cap, beginning January 1, 2024. The rebate was previously capped at 100% of a drug’s average manufacturer price.

Additionally, there has been heightened governmental scrutiny in the United States of pharmaceutical pricing practices in light of the rising cost of prescription drugs and biologics. Such scrutiny has resulted in several recent Congressional inquiries, presidential executive orders and proposed and enacted federal and state legislation and regulations designed to, among other things, reduce the cost of prescription drugs under Medicare, bring more transparency to product pricing, review the relationship between pricing and manufacturer patient assistance programs, and reform government program reimbursement methodologies for products. Most significantly, in August 2022, the Inflation Reduction Act of 2022 (“IRA”) was enacted. This statute marks the most significant action by Congress with respect to the pharmaceutical industry since adoption of the ACA in 2010. Among other things, the IRA requires manufacturers of certain drugs to engage in price negotiations with Medicare to establish a “maximum fair price” for a fixed number of pharmaceutical and biological products covered under Medicare Parts B and D; imposes rebates under Medicare Part B and Medicare Part D to penalize price increases that outpace inflation (first due in 2023); redesigns the Medicare Part D benefit (beginning in 2024); and replaces the Part D coverage gap discount program with a new manufacturer discounting program (which began in 2025). CMS published the negotiated maximum prices for the initial ten drugs that were subject to the IRA’s negotiation process, which are effective in 2026, and published the negotiated maximum prices for the subsequent 15 drugs to be effective in 2027. The IRA permits the Secretary of the Department of Health and Human Services (“HHS”) to implement many of these provisions through guidance, as opposed to regulation, for the initial years. HHS has and will continue to issue and update guidance as these programs are implemented, although the Medicare drug price negotiation program is currently subject to legal challenges. In December 2023, the National Institute of Standards and Technology published for comment a Draft Interagency Guidance Framework for Considering the Exercise of March-In Rights, which, under the Bayh-Dole Act, gives the federal government authority to “march in” and grant compulsory patent licenses to third parties in some circumstances. Under the draft guidance, march-in rights include the price of a product as one factor an agency can use when deciding to exercise march-in rights. While march-in rights have not previously been exercised, it is uncertain if that will continue under the new framework. The impact of the IRA on the pharmaceutical industry cannot yet be fully determined but is likely to be significant. Further, there is uncertainty surrounding this program with the current U.S. presidential administration, especially in light of the administration’s budget cuts which impact an agency’s ability to regulate through guidance. Further, it is unclear how the new leadership of HHS, CMS, etc. will approach the issue of drug pricing. Additional drug pricing proposals could appear in future legislation.

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At the state level, legislatures have increasingly passed legislation and implemented regulations designed to control pharmaceutical and biological product pricing, including price or reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure, drug price reporting, and other transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing. Some states have enacted legislation creating so-called prescription drug affordability boards, which ultimately may attempt to impose price limits on certain drugs in these states, while some states are also seeking to implement general, across-the-board price caps for pharmaceuticals, or are seeking to regulate drug distribution. Legally mandated price controls on payment amounts by third-party payors or other restrictions could harm Boundless Bio’s business, results of operations, financial condition, and prospects. In addition, regional healthcare authorities and individual hospitals are increasingly using bidding procedures to determine what pharmaceutical products and which suppliers will be included in their prescription drug and other healthcare programs. This could reduce the ultimate demand for Boundless Bio’s ecDTx, if approved, or put pressure on Boundless Bio’s product pricing, which could negatively affect Boundless Bio’s business, results of operations, financial condition, and prospects.

The future course of federal or state healthcare legislation and regulation in the U.S. directed at broadening the availability of healthcare and containing or lowering the cost of healthcare, is subject to considerable uncertainty. The current presidential administration is pursuing policies to reduce regulations and expenditures across the federal government, including at HHS, the FDA, the CMS, and related agencies. These actions, presently directed by executive orders or memoranda from the Office of Management and Budget, may propose policy changes that create additional uncertainty for the pharmaceutical industry and Boundless Bio’s business. These actions and proposals include, for example, (a) reducing agency workforce and cutting programs; (b) rescinding a prior presidential administration’s executive order tasking the Center for Medicare and Medicaid Innovation to consider new payment and healthcare models to limit drug spending; (c) directing HHS and other agencies to lower prescription drug costs through a variety of initiatives, including by improving upon the Medicare Drug Price Negotiation Program and establishing most-favored-nation pricing for pharmaceutical products; (d) imposing tariffs of imported pharmaceutical products; and (e) directing certain federal agencies to enforce existing law regarding hospital and price plan price transparency and by standardizing prices across hospitals and health plans. Additionally, in its June 2024 decision in Loper Bright Enterprises v. Raimondo, or Loper Bright, the U.S. Supreme Court overturned the longstanding Chevron doctrine, under which courts were required to give deference to regulatory agencies’ reasonable interpretations of ambiguous federal statutes. The Loper Bright decision could result in additional legal challenges to current regulations and guidance issued by federal agencies applicable to Boundless Bio’s operations, including those issued by the FDA. The U.S. Congress may introduce and ultimately pass healthcare related legislation that could, among others, impact the drug approval process and make changes to modify the Medicare Drug Price Negotiation Program created under the IRA.

If the Merger is not completed and Boundless Bio continues to develop any ecDTx, Boundless Bio expects that these existing laws and other healthcare reform measures that may be adopted in the future may result in additional reductions in Medicare and other healthcare funding, more rigorous coverage criteria, new payment methodologies, and additional downward pressure on the price that Boundless Bio receives for any approved product. In addition, Boundless Bio expects to experience pricing pressures in connection with the sale of Boundless Bio’s product candidates due to the trend toward managed healthcare, the increasing influence of health maintenance organizations and additional legislative changes. Any reduction in reimbursement from Medicare or other government programs may result in a similar reduction in payments from private payors. The implementation of cost containment measures or other healthcare reforms may prevent Boundless Bio from being able to generate revenue, attain profitability, or commercialize its ecDTx, if approved.

If product liability lawsuits are brought against Boundless Bio, it may incur substantial liabilities and may be required to limit, delay, or cease commercialization of any ecDTx.

Boundless Bio faces an inherent risk of product liability as a result of any clinical trials of Boundless Bio’s ecDTx and will face an even greater risk if Boundless Bio commercializes any ecDTx, if approved. For example,

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Boundless Bio may be sued if any ecDTx allegedly cause injury or are found to be otherwise unsuitable during product testing, manufacturing, marketing, or sale. Any such product liability claims may include allegations of defects in manufacturing, defects in design, a failure to warn of dangers inherent in the ecDTx, negligence, strict liability, and a breach of warranties. Claims may be brought against Boundless Bio by clinical trial participants, patients or others using, administering, or selling products that may be approved in the future. Claims could also be asserted under state consumer protection acts.

If Boundless Bio cannot successfully defend itself against product liability claims, Boundless Bio may incur substantial liabilities or be required to limit, delay, or cease the commercialization of its products. Even a successful defense would require significant financial and management resources. Regardless of the merits or eventual outcome, liability claims may result in:

Boundless Bio currently holds approximately $10.0 million in product liability insurance coverage in the aggregate. Boundless Bio may need to increase its insurance coverage if Boundless Bio continues to develop any ecDTx and Boundless Bio expands its clinical trials or if Boundless Bio commences commercialization of its ecDTx. Insurance coverage is increasingly expensive. Boundless Bio’s inability to obtain and retain sufficient product liability insurance at an acceptable cost to protect against potential product liability claims could prevent or inhibit the commercialization of Boundless Bio’s ecDTx. Although Boundless Bio will maintain such insurance, any claim that may be brought against it could result in a court judgment or settlement in an amount that is not covered, in whole or in part, by its insurance or that is in excess of the limits of Boundless Bio’s insurance coverage. Boundless Bio’s insurance policies will also have various exclusions, and Boundless Bio may be subject to a product liability claim for which it has no coverage. Boundless Bio may have to pay any amounts awarded by a court or negotiated in a settlement that exceed its coverage limitations or that are not covered by its insurance, and Boundless Bio may not have, or be able to obtain, sufficient capital to pay such amounts.

Boundless Bio’s insurance policies are expensive and protect Boundless Bio from only some business risks, which will leave Boundless Bio exposed to significant uninsured liabilities.

Boundless Bio does not carry insurance for all categories of risk that Boundless Bio’s business may encounter. Some of the policies Boundless Bio currently maintains include property, general liability, employee benefits liability, business automobile, workers’ compensation, products/clinical trial liability, cyber liability, clinical trials, and directors’ and officers’, and employment practices insurance. Boundless Bio does not know, however, if Boundless Bio will be able to maintain insurance with adequate levels of coverage. No assurance can be given that an insurance carrier will not seek to cancel or deny coverage after a claim has occurred. Any significant uninsured liability may require Boundless Bio to pay substantial amounts, which would adversely affect Boundless Bio’s financial position and results of operations.

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Boundless Bio and its service providers may be subject to a variety of data protection, privacy, and security obligations, including laws, regulations, standards, and contractual provisions, which could increase compliance costs, and Boundless Bio’s actual or perceived failure to comply with such laws and obligations could subject Boundless Bio to potentially significant liability, fines, or penalties and otherwise harm its business.

Boundless Bio and its service providers may maintain a large quantity of sensitive information, including confidential business and patient health information, in connection with any clinical trials, and are subject to laws and regulations governing the privacy and security of such information. The global data protection landscape is rapidly evolving, and Boundless Bio and its service providers may be affected by or subject to existing, amended, or new laws and regulations in the future, including as its operations continue to expand or if Boundless Bio operates in foreign jurisdictions. These laws and regulations may be subject to differing interpretations, thus creating potentially complex compliance issues for Boundless Bio and its service providers, strategic partners, and future customers. The cost of compliance with these laws, regulations, and standards is high and is likely to increase in the future. Any failure or perceived failure by Boundless Bio to comply with federal, state, or foreign laws or regulations, its internal policies and procedures or its contracts governing Boundless Bio’s processing of personal information could result in negative publicity, government investigations and enforcement actions, claims by third parties, and damage to Boundless Bio’s reputation, any of which could have a material adverse effect on Boundless Bio’s business, financial condition, results of operations, and prospects.

If Boundless Bio continues to develop any ecDTx and Boundless Bio’s operations and business grow, Boundless Bio may become subject to or affected by new or additional data protection laws and regulations and face increased scrutiny or attention from regulatory authorities. In the United States, numerous federal and state laws and regulations, including health information privacy laws, data breach notification laws, and consumer protection laws, that govern the collection, use, storage, transfer, disclosure, protection, and other processing of health-related and other personal information could apply to Boundless Bio’s operations or the operations of Boundless Bio’s collaborators and third-party providers. In addition, Boundless Bio may obtain health information from third parties (including research institutions from which Boundless Bio obtains clinical trial data) that are subject to privacy and security requirements under HIPAA, as amended by HITECH. Consequently, depending on the facts and circumstances, Boundless Bio could be subject to significant penalties if Boundless Bio knowingly receive individually identifiable health information from a HIPAA-covered healthcare provider or research institution that has not satisfied HIPAA’s requirements for disclosure of individually identifiable health information.

In addition, certain state laws govern the privacy and security of health-related and other personal information, many of which may differ from each other and from HIPAA, thus, complicating compliance efforts. Failure to comply with these laws, where applicable, can result in the imposition of significant civil and/or criminal penalties and private litigation. By way of example, the California Consumer Privacy Act, as amended by the California Privacy Rights Act (collectively, the “CCPA”), requires covered businesses that process the personal information of California residents to, among other things: (i) provide certain disclosures to California residents regarding the business’s collection, use, and disclosure of their personal information; (ii) receive and respond to requests from California residents to access, delete, and correct their personal information, or to opt out of certain disclosures of their personal information; and (iii) enter into specific contractual provisions with service providers that process California resident personal information on the business’s behalf. Additional compliance investment and potential business process changes may be required. Similar laws have been passed in other states and are continuing to be proposed at the state and federal level, reflecting a trend toward more stringent privacy legislation in the United States. In the event that Boundless Bio is subject to or affected by HIPAA, the CCPA, or other domestic privacy and data protection laws, any liability from failure to comply with the requirements of these laws could adversely affect Boundless Bio’s financial condition.

In addition to the state comprehensive data privacy laws, recent years have brought substantial changes to the federal and state treatment of non-HIPAA consumer health information. The Federal Trade Commission (“FTC”) and many state Attorneys General continue to enforce federal and state consumer protection laws

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against companies for online collection, use, dissemination, and security practices that appear to be unfair or deceptive. The FTC brought three enforcement actions in 2023 against a range of companies that handle electronic health information relating to collection and disclosure of non-HIPAA covered consumer health information under Section 5 of the FTC Act, two of which included allegations made under the FTC’s Health Breach Notification Rule (“HBNR”). The FTC’s focus on health information continued in 2024 with changes to the HBNR that clarified its scope and emphasized applicability to non-HIPAA healthcare providers as well as three additional enforcement actions against companies for their use of health information for advertising purposes. At the state level, Washington and Nevada have adopted significant new legislation addressing businesses treatment of consumer health information, and Connecticut added more stringent protections for health information to its existing comprehensive state privacy law. In both Washington’s and Nevada’s laws, there are restrictive provisions limiting collection and disclosure of consumer health information, and Washington’s law provides a separate private right of action for violations.

There are also privacy laws in other countries that may impact Boundless Bio’s operations, now or in the future. For example, in Europe, the General Data Protection Regulation (“GDPR”) went into effect in May 2018, and imposes stringent requirements regarding the collection, use, disclosure, storage, transfer, or other processing of personal data of individuals within the European Economic Area (“EEA”). Companies that must comply with the GDPR face increased compliance obligations and risk, including more robust regulatory enforcement of data protection requirements and potential fines for noncompliance of up to €20 million or 4% of the annual global revenue of the noncompliant company, whichever is greater. The GDPR also confers a private right of action in some circumstances on data subjects and consumer associations to lodge complaints with supervisory authorities, seek judicial remedies, and obtain compensation for damages resulting from violations of the GDPR. In addition to fines, a breach of the GDPR may result in regulatory investigations, reputational damage, orders to cease or change Boundless Bio’s data processing activities, enforcement notices, assessment notices (for a compulsory audit), and/or civil claims (including class actions).

Among other requirements, the GDPR regulates transfers of personal data subject to the GDPR to third countries that have not been found to provide adequate protection to such personal data, including the United States, and the efficacy and longevity of current transfer mechanisms between the EEA and the United States remains uncertain. Case law from the Court of Justice of the European Union (“CJEU”) states that reliance on the standard contractual clauses-a standard form of contract approved by the European Commission as an adequate personal data transfer mechanism alone may not necessarily be sufficient in all circumstances and that transfers must be assessed on a case-by-case basis. On July 10, 2023, the European Commission adopted its Adequacy Decision in relation to the new EU-US Data Privacy Framework (“DPF”), rendering the DPF effective as a GDPR transfer mechanism to U.S. entities self-certified under the DPF. Boundless Bio expects the existing legal complexity and uncertainty regarding international personal data transfers to continue. In particular, Boundless Bio expects the DPF Adequacy Decision to be challenged, and international transfers to the United States and to other jurisdictions more generally to continue to be subject to enhanced scrutiny by regulators. As a result, Boundless Bio may have to make certain operational changes and Boundless Bio will have to implement revised standard contractual clauses and other relevant documentation for existing data transfers within required time frames.

Further, following the withdrawal of the United Kingdom from the European Union and the end of the transition period, from January 1, 2021, companies could also be subject to the United Kingdom General Data Protection Regulation and Data Protection Act 2018 (collectively, the “UK GDPR”). The UK GDPR mirrors the fines under the GDPR and has the ability to fine up to the greater of €20 million/£17 million or 4% of global turnover. On October 12, 2023, the UK Extension to the DPF came into effect (as approved by the UK Government), as a data transfer mechanism from the UK to U.S. entities self-certified under the DPF. If Boundless Bio expands into other foreign countries and jurisdictions, Boundless Bio may be subject to additional laws and regulations that may affect how Boundless Bio conducts business.

Compliance with U.S. and international data protection laws and regulations could require Boundless Bio to take on more onerous obligations in its contracts, restrict its ability to collect, store, use, transfer, disclose, and

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otherwise process data, update its data privacy and security policies and procedures, or in some cases, impact its ability to operate in certain jurisdictions. Failure or perceived failure by Boundless Bio or its collaborators and its service providers to comply with U.S. and international data protection laws and regulations could result in government enforcement actions (which could include civil or criminal penalties), private litigation, and/or adverse publicity and could negatively affect Boundless Bio’s operating results and business. Moreover, clinical trial subjects about whom Boundless Bio or its potential collaborators obtain information, as well as the providers who share this information with Boundless Bio, may contractually limit Boundless Bio’s ability to use and disclose such information. Claims that Boundless Bio has violated individuals’ privacy rights, failed to comply with data protection laws, or breached its contractual obligations, even if Boundless Bio is not found liable, could be expensive and time consuming to defend, could result in adverse publicity, and adversely affect Boundless Bio’s business, financial condition, results of operations, and prospects.

Boundless Bio’s information technology systems, or those of any of Boundless Bio’s service providers, may fail or suffer security incidents and other disruptions, which could result in a material disruption of its ecDTx development programs if Boundless Bio continues to develop any ecDTx, compromise sensitive information related to Boundless Bio’s business, or prevent Boundless Bio from accessing critical information, potentially exposing Boundless Bio to liability, or otherwise adversely affecting Boundless Bio’s business.

In the ordinary course of business, Boundless Bio collects, stores, and transmits confidential information including but not limited to intellectual property, clinical trial data, proprietary and confidential business information, and personal information of Boundless Bio’s employees and contractors (collectively, “Confidential Information”). Boundless Bio’s information technology systems and those of Boundless Bio’s third-party service providers, strategic partners, and other contractors or consultants are vulnerable to attack, damage, and interruption from computer viruses and malware (e.g. ransomware), malicious code, misconfigurations, “bugs” or other vulnerabilities, natural disasters, terrorism, war, telecommunication and electrical failures, hacking, cyberattacks, phishing attacks and other social engineering schemes, employee theft or misuse, human error, fraud, denial or degradation of service attacks, and sophisticated nation-state and nation-state-supported actors. In addition, attacks upon information technology systems are increasing in their frequency, levels of persistence, sophistication, and intensity, and are being conducted by sophisticated and organized groups and individuals with a wide range of motives and expertise. Furthermore, because the techniques used to obtain unauthorized access to, or to sabotage, systems change frequently and often are not recognized until launched against a target, Boundless Bio may be unable to anticipate these techniques or implement adequate preventative measures. Boundless Bio may also experience security incidents that may remain undetected for an extended period. Even if identified, Boundless Bio may be unable to adequately investigate or remediate incidents or breaches due to attackers increasingly using tools and techniques that are designed to circumvent controls, to avoid detection, and to remove or obfuscate forensic evidence. There can also be no assurance that Boundless Bio’s and its third-party service providers’, strategic partners’, contractors’, or consultants’ cybersecurity risk management program and processes, including policies, controls, or procedures, will be fully implemented, complied with or effective in protecting Boundless Bio’s systems, networks, and Confidential Information.

Boundless Bio and certain of Boundless Bio’s service providers are from time to time subject to cyberattacks and security incidents. If any such event, whether actual or perceived, were to occur, it could impact Boundless Bio’s reputation and/or operations, cause Boundless Bio to incur significant costs, including legal expenses, harm customer confidence, hurt Boundless Bio’s expansion into new markets, cause Boundless Bio to incur remediation costs, or cause Boundless Bio to lose existing customers. For example, any loss of clinical trial data from clinical trials could result in delays in Boundless Bio’s regulatory approval efforts and significantly increase Boundless Bio’s costs to recover or reproduce the data. Boundless Bio also relies on a third party to manufacture its ecDTx, and similar events relating to their computer systems could also have a material adverse effect on Boundless Bio’s business. To the extent that any actual or perceived disruption or security incident affects Boundless Bio’s systems (or those of its third-party collaborators, service providers, contractors or consultants) or were to result in a loss of or accidental, unlawful, or unauthorized access to, use of, release of, or other processing of Confidential Information, Boundless Bio could incur liability, the further development and

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commercialization of its ecDTx could be delayed, and Boundless Bio could be subject to significant fines, penalties or liabilities for any noncompliance to certain privacy and security laws.

Boundless Bio has also outsourced elements of its information technology infrastructure, and as a result a number of third-party vendors may or could have access to Boundless Bio’s Confidential Information. If Boundless Bio’s third-party vendors fail to protect their information technology systems and Boundless Bio’s Confidential Information, Boundless Bio may be vulnerable to disruptions in service and unauthorized access to its Confidential Information and Boundless Bio could incur liability and reputational damage. If the information technology systems of Boundless Bio’s third-party vendors and other contractors and consultants become subject to disruptions or security breaches, Boundless Bio may have insufficient recourse against such third parties and Boundless Bio may have to expend significant resources to mitigate the impact of such an event, and to develop and implement protections to prevent future events of this nature from occurring. Some of the federal, state, and foreign government requirements include obligations of companies to notify individuals of security breaches involving particular categories of personally identifiable information, which could result from incidents experienced by Boundless Bio or by Boundless Bio’s vendors, contractors, or organizations with which Boundless Bio has formed strategic relationships. Any adverse impact to the availability, integrity, or confidentiality of Boundless Bio’s or third-party systems or Confidential Information can result in legal claims or proceedings (such as class actions), regulatory investigations and enforcement actions, fines, and penalties. Boundless Bio’s contracts may not contain limitations of liability, and even where they do, there can be no assurance that limitations of liability in Boundless Bio’s contracts are sufficient to protect Boundless Bio from liabilities, damages, or claims related to Boundless Bio’s data privacy and security obligations. Although Boundless Bio currently holds cybersecurity insurance, the costs related to significant security breaches or disruptions could be material and cause Boundless Bio to incur significant expenses.

Boundless Bio’s business is subject to risks arising from pandemic and epidemic diseases.

The COVID-19 worldwide pandemic presented substantial public health and economic challenges and affected Boundless Bio’s employees, patients, physicians and other healthcare providers, communities, and business operations, as well as the U.S. and global economies and financial markets. If Boundless Bio continues to develop any ecDTx, any future pandemic or epidemic disease outbreaks could disrupt the supply chain and the manufacture or shipment of drug substances and finished drug products for Boundless Bio’s ecDTx for use in its clinical trials and research and preclinical studies and, delay, limit or prevent its employees and CROs from continuing research and development activities, impede its clinical trial initiation and recruitment and the ability of patients to continue in clinical trials, alter the results of the clinical trial based on participants contracting the disease or otherwise increasing the number of observed adverse events, impede testing, monitoring, data collection and analysis and other related activities, any of which could delay Boundless Bio’s preclinical studies and clinical trials and increase Boundless Bio’s development costs, and have a material adverse effect on Boundless Bio’s business, financial condition, and results of operations. Any future pandemic or epidemic disease outbreak could also potentially further affect the business of the FDA, the European Medicines Agency (“EMA”), or other regulatory authorities, which could result in delays in meetings related to any of Boundless Bio’s clinical trials, as well have an adverse impact on global economic conditions, which could have an adverse effect on Boundless Bio’s business and financial condition, including impairing its ability to raise capital when needed.

Boundless Bio’s business could be affected by litigation, government investigations, and enforcement actions.

Boundless Bio operates in a number of jurisdictions in a highly regulated industry, and Boundless Bio could be subject to litigation, government investigation, and enforcement actions on a variety of matters in the United States or foreign jurisdictions, including, without limitation, intellectual property, regulatory, product liability, environmental, whistleblower, false claims, privacy, anti-kickback, anti-bribery, securities, commercial, employment, and other claims and legal proceedings that may arise from conducting Boundless Bio’s business. Any determination that Boundless Bio’s operations or activities are not in compliance with existing laws or regulations could result in the imposition of fines, civil and criminal penalties, equitable remedies, including

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disgorgement, injunctive relief, and/or other sanctions against Boundless Bio, and remediation of any such findings could have an adverse effect on Boundless Bio’s business operations.

Legal proceedings, government investigations, and enforcement actions can be expensive and time-consuming. An adverse outcome resulting from any such proceedings, investigations or enforcement actions could result in significant damages awards, fines, penalties, exclusion from the federal healthcare programs, healthcare debarment, injunctive relief, product recalls, reputational damage, and modifications of Boundless Bio’s business practices, which could have a material adverse effect on Boundless Bio’s business and results of operations. Even if such a proceeding, investigation, or enforcement action is ultimately decided in Boundless Bio’s favor, the investigation and defense thereof could require substantial financial and management resources.

Boundless Bio’s employees and independent contractors, including principal investigators, CROs, consultants, and vendors, may engage in misconduct or other improper activities, including noncompliance with regulatory standards and requirements.

Boundless Bio is exposed to the risk that Boundless Bio’s employees and independent contractors, including principal investigators, CROs, consultants, and vendors may engage in misconduct or other illegal activity. Misconduct by these parties could include intentional, reckless, and/or negligent conduct or disclosure of unauthorized activities to Boundless Bio that violate: (i) the laws and regulations of the FDA and other similar regulatory requirements, including those laws that require the reporting of true, complete, and accurate information to such authorities, (ii) manufacturing standards, including cGMP requirements, (iii) federal and state data privacy, security, fraud, and abuse and other healthcare laws and regulations in the United States and abroad (iv) laws that require the true, complete, and accurate reporting of financial information or data, or (v) laws that prohibit insider trading. Activities subject to these laws also involve the improper use or misrepresentation of information obtained in the course of clinical trials, the creation of fraudulent data in Boundless Bio’s preclinical studies or clinical trials, or illegal misappropriation of drug product, which could result in regulatory sanctions and cause serious harm to Boundless Bio’s reputation. It is not always possible to identify and deter misconduct by employees and other third parties, and the precautions Boundless Bio takes to detect and prevent this activity may not be effective in controlling unknown or unmanaged risks or losses or in protecting Boundless Bio from governmental investigations or other actions or lawsuits stemming from a failure to be in compliance with such laws or regulations. In addition, Boundless Bio is subject to the risk that a person or government could allege such fraud or other misconduct, even if none occurred. If any such actions are instituted against Boundless Bio, and it is not successful in defending itself or asserting Boundless Bio’s rights, those actions could have a significant impact on Boundless Bio’s business and financial results, including, without limitation, the imposition of significant civil, criminal, and administrative penalties, damages, monetary fines, disgorgements, possible exclusion from participation in Medicare, Medicaid and other federal healthcare programs, imprisonment, contractual damages, reputational harm, diminished profits and future earnings, additional reporting requirements and oversight if Boundless Bio becomes subject to a corporate integrity agreement or similar agreement to resolve allegations of non-compliance with these laws, and curtailment of Boundless Bio’s operations, any of which could adversely affect Boundless Bio’s ability to operate Boundless Bio’s business and Boundless Bio’s results of operations.

If the Merger is not completed, Boundless Bio may engage in strategic transactions that could impact Boundless Bio’s liquidity, increase Boundless Bio’s expenses, and present significant distractions to Boundless Bio’s management.

If the Merger is not completed, from time to time, Boundless Bio may consider strategic transactions, such as acquisitions of companies, asset purchases, and out-licensing or in-licensing of intellectual property, products, or technologies. Additional potential transactions that Boundless Bio may consider in the future if the Merger is not completed include a variety of business arrangements, including spin-offs, strategic partnerships, joint ventures, restructurings, divestitures, business combinations, and investments. Any future transactions could increase Boundless Bio’s near and long-term expenditures, result in potentially dilutive issuances of its equity

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securities, including Boundless Bio Common Stock, or the incurrence of debt, contingent liabilities, amortization expenses or acquired in-process research and development expenses, any of which could affect Boundless Bio’s financial condition, liquidity, and results of operations. Future acquisitions may also require Boundless Bio to obtain additional financing, which may not be available on favorable terms or at all. These transactions may never be successful and may require significant time and attention of Boundless Bio’s management. In addition, the integration of any business that Boundless Bio may acquire in the future may disrupt Boundless Bio’s existing business and may be a complex, risky, and costly endeavor for which Boundless Bio may never realize the full benefits. Furthermore, Boundless Bio may experience losses related to investments in other companies, including as a result of failure to realize expected benefits or the materialization of unexpected liabilities or risks, which could have a material negative effect on Boundless Bio’s results of operations and financial condition. Accordingly, although there can be no assurance that Boundless Bio will undertake or successfully complete any additional transactions of the nature described above, any additional transactions that Boundless Bio does complete could have a material adverse effect on Boundless Bio’s business, results of operations, financial condition, and prospects.

Boundless Bio’s ability to use net operating loss carryforwards and other tax attributes may be limited.

Boundless Bio has incurred substantial losses during Boundless Bio’s history, does not expect to become profitable in the near future, and may never achieve profitability. To the extent that Boundless Bio continues to generate taxable losses, unused losses will carry forward to offset future taxable income, if any (subject to limitations), until such unused losses expire (if at all). As of December 31, 2025, Boundless Bio had net operating loss (“NOL”) carryforwards of approximately $161.4 million for federal income tax purposes and $231.3 million for state income tax purposes, which may be available to offset Boundless Bio’s future taxable income, if any. Boundless Bio’s federal NOL carryforwards will not expire but may generally be used to offset only 80% of taxable income, which may require Boundless Bio to pay federal income taxes in future years despite having additional federal NOL carryforwards to utilize. Boundless Bio’s state NOL carryforwards begin to expire in various amounts in 2038. As of December 31, 2025, Boundless Bio had federal and state research and development tax credit carryforwards of approximately $9.3 million and $5.9 million, respectively. Boundless Bio’s NOL carryforwards and other tax attributes are subject to review and possible adjustment by the Internal Revenue Service (“IRS”) and state tax authorities.

In addition, under Section 382 of the Code, Boundless Bio’s federal NOL carryforwards may be or become subject to an annual limitation in the event Boundless Bio has had or has in the future an “ownership change.” For these purposes, an “ownership change” generally occurs if one or more stockholders or groups of stockholders who own at least 5% of a company’s stock increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period. Similar rules may apply under state tax laws. Boundless Bio has not determined the amount of the cumulative change in Boundless Bio’s ownership resulting from Boundless Bio’s IPO, the Merger or other transactions, or any resulting limitations on Boundless Bio’s ability to utilize Boundless Bio’s NOL carryforwards and other tax attributes. However, Boundless Bio believes that its ability to utilize Boundless Bio’s NOL carryforwards and other tax attributes to offset future taxable income or tax liabilities may be limited as a result of ownership changes, including potential changes in connection with Boundless Bio’s IPO or the Merger. If Boundless Bio earns taxable income, such limitations could result in increased future income tax liability to Boundless Bio, and its future cash flows could be adversely affected. Boundless Bio has recorded a full valuation allowance related to Boundless Bio’s NOL carryforwards and other deferred tax assets due to the uncertainty of the ultimate realization of the future benefits of those assets.

Inflation could adversely affect Boundless Bio’s business and results of operation.

While inflation in the United States has been relatively low in recent years, the economy in the United States encountered a material level of inflation since 2021. Although inflation eased somewhat in 2024, it has raised Boundless Bio’s costs for commodities, labor, materials, and services and other costs required to grow and

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operate its business, and failure to secure these on reasonable terms may adversely impact Boundless Bio’s financial condition. Additionally, increases in inflation, along with public health concerns, geopolitical developments, and global supply chain disruptions, have caused, and may in the future cause, global economic uncertainty, and uncertainty about the interest rate environment, which may make it more difficult, costly, or dilutive for Boundless Bio to secure additional financing. A failure to adequately respond to these risks could have a material adverse impact on Boundless Bio’s financial condition and results of operations.

Risks Related to Boundless Bio’s Intellectual Property

If Boundless Bio is unable to obtain, maintain, defend, and enforce patent or other intellectual property protection for its ecDTx, diagnostic, or technology, or if the scope of the patent or other intellectual property protection obtained is not sufficiently broad, Boundless Bio’s competitors or other third parties could develop and commercialize products similar or identical to Boundless Bio’s, and Boundless Bio’s ability to successfully commercialize any ecDTx may be adversely affected.

Boundless Bio relies upon a combination of patent, trade secret, and trademark protection for its ecDTx, its diagnostic, and proprietary technologies to prevent third parties from exploiting its achievements, thus eroding Boundless Bio’s competitive position in its market. These legal measures afford only limited protection, and competitors or others may gain access to or use Boundless Bio’s intellectual property and proprietary information. Boundless Bio’s success depends in large part on its ability to obtain, maintain, expand, enforce, and defend the scope of Boundless Bio’s intellectual property protection in the United States and other countries with respect to its ecDTx, its diagnostic, and other proprietary technologies Boundless Bio may develop. Boundless Bio generally seeks to protect its proprietary position, in part, by filing patent applications in the United States and abroad relating to its ecDTx and diagnostics, manufacturing processes, and methods of use. Boundless Bio may also seek to protect its proprietary position by acquiring or in-licensing relevant issued patents or pending patent applications from third parties. If Boundless Bio is unable to obtain, maintain, expand, enforce, and defend the scope of its intellectual property protection, Boundless Bio’s business, financial condition, results of operations, and prospects could be materially harmed.

Changes in either the patent laws or their interpretation in the United States and other jurisdictions may diminish Boundless Bio’s ability to protect its intellectual property, obtain, maintain, expand, enforce, and defend Boundless Bio’s intellectual property rights and, more generally, could affect the value of Boundless Bio’s intellectual property or narrow the scope of its protection. Boundless Bio cannot predict whether the patent applications Boundless Bio currently or may in the future pursue or may in-license will issue as patents in any particular jurisdiction, whether the claims of any issued patents will provide sufficient protection against competitors or other third parties, or if these patents are challenged by Boundless Bio’s competitors, whether the patents will be found to be invalid, unenforceable, or not infringed.

The patent prosecution process is expensive, time-consuming, and complex, and Boundless Bio may not be able to file, prosecute, maintain, enforce, defend, or license all necessary or desirable patent applications or patents at a reasonable cost or in a timely manner or in all jurisdictions. If Boundless Bio is unable to adequately fund its patent prosecution and maintenance, or if the costs of defending its patents against third-party challenges become prohibitive, Boundless Bio’s competitive position could be weakened. Additionally, recent reforms and changes at government agencies of the United States and those of non-U.S. jurisdictions could increase the uncertainties and costs surrounding the prosecution or maintenance of Boundless Bio’s patent applications, and the maintenance, enforcement, or defense of Boundless Bio’s issued patents. For example, the ability of the U.S. Patent and Trademark Office (“USPTO”) and other applicable patent authorities to properly administer their functions is highly dependent on the levels of funding available to the agency and their ability to retain key personnel and fill key leadership appointments, among various factors. Termination of employees or delays in replacing or hiring for key positions could significantly impact the ability of the USPTO and other applicable patent authorities to fulfill their functions and could greatly impact Boundless Bio’s ability to timely and adequately prosecute or maintain Boundless Bio’s patent applications, and Boundless Bio’s ability to timely and adequately maintain, enforce, or defend Boundless Bio’s issued patents. It is also possible that Boundless Bio

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will fail to identify patentable aspects of Boundless Bio’s research and development output in time to obtain patent protection. Although Boundless Bio enters into non-disclosure and confidentiality agreements with parties who have access to confidential or patentable aspects of Boundless Bio’s research and development output, such as Boundless Bio’s employees, third-party collaborators, CROs, contract manufacturers, consultants, advisors, and other third parties, any of these parties may breach the agreements and disclose such output before a patent application is filed, thereby jeopardizing Boundless Bio’s ability to seek patent protection. Consequently, Boundless Bio may not be able to prevent any third party from using any of Boundless Bio’s technology that is in the public domain to compete with its ecDTx or technologies. In addition, Boundless Bio’s ability to obtain and maintain valid and enforceable patents depends on whether the differences between Boundless Bio’s inventions and the prior art allow Boundless Bio’s inventions to be patentable in light of the prior art. Furthermore, publications of discoveries in the scientific literature often lag behind the actual discoveries, and patent applications in the United States and other jurisdictions are typically not published until 18 months after filing, or in some cases not at all. Therefore, Boundless Bio cannot be certain that it was the first to invent the inventions claimed in any of Boundless Bio’s owned patents or pending patent applications, or that Boundless Bio or any future licensors were the first to file for patent protection of such inventions. If a third party can establish that Boundless Bio was not the first to make or the first to file for patent protection of such inventions, Boundless Bio’s patents and patent applications may not issue as patents and even if issued, may be challenged and invalidated or rendered unenforceable.

The patent position of biopharmaceutical companies generally is highly uncertain, involves complex legal and factual questions, and has been the subject of much litigation in recent years. As a result, the issuance, scope, validity, enforceability, and commercial value of Boundless Bio’s patent rights are highly uncertain. Boundless Bio’s current and future patent applications may not result in patents being issued.

Any issued patents may not afford sufficient protection of Boundless Bio’s ecDTx or their intended uses against competitors, nor can there be any assurance that the patents issued will not be infringed, designed around, invalidated by third parties, or effectively prevent others from commercializing competitive technologies or products. Further, even if these patents are granted, they may be difficult to enforce. Obtaining and maintaining Boundless Bio’s patent protection depends on compliance with various procedural, document submission, fee payment, and other requirements imposed by governmental patent agencies, and Boundless Bio’s patent protection could be reduced or eliminated if Boundless Bio fails to comply with these requirements. In the event Boundless Bio experiences noncompliance events that cannot be corrected and Boundless Bio loses its patent rights, competitors could enter the market, which would have a material adverse effect on Boundless Bio’s business. Further, any issued patents that Boundless Bio owns or may license in the future covering Boundless Bio’s ecDTx could be narrowed or found invalid or unenforceable if challenged in court or before administrative bodies in the United States or other countries, including the USPTO. Also, patent terms, including any extensions or adjustments that may or may not be available to Boundless Bio, may be inadequate to protect Boundless Bio’s competitive position on its ecDTx for an adequate amount of time, and Boundless Bio may be subject to claims challenging the inventorship, validity, or enforceability of Boundless Bio’s patents and/or other intellectual property. Changes in United States patent law, or laws in other countries, could diminish the value of patents in general, thereby impairing Boundless Bio’s ability to protect its ecDTx. Further, if Boundless Bio encounters delays in Boundless Bio’s development and testing of any ecDTx, clinical trials, or regulatory review and approval of its ecDTx, the period of time during which Boundless Bio could market Boundless Bio’s ecDTx under patent protection may be reduced (i.e., patents protecting the ecDTx might expire before or shortly after such ecDTx are commercialized). Thus, Boundless Bio’s patents may not provide Boundless Bio with sufficient rights to exclude others from commercializing products similar or identical to Boundless Bio’s or afford Boundless Bio any meaningful competitive advantage.

Moreover, the claim coverage in a patent application can be significantly reduced before the corresponding patent is granted. Even if patent applications issue as patents, they may not issue in a form that will provide Boundless Bio with any meaningful protection, prevent competitors or other third parties from competing with Boundless Bio, or otherwise provide Boundless Bio with any competitive advantage. Any patents issuing from

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Boundless Bio’s owned and any future in-licensed patent applications may be challenged, narrowed, circumvented, or invalidated by third parties. Consequently, Boundless Bio does not know whether Boundless Bio’s ecDTx and other proprietary technology will be protectable or remain protected by valid and enforceable patents. Even if a patent is granted, Boundless Bio’s competitors or other third parties may be able to circumvent the patent by developing similar or alternative technologies or products in a non-infringing manner, which could materially adversely affect Boundless Bio’s business, financial condition, results of operations, and prospects. Furthermore, Boundless Bio’s competitors or other third parties may avail themselves of safe harbors under the Drug Price Competition and Patent Term Restoration Act of 1984 (“Hatch-Waxman Amendments”) to conduct research and clinical trials.

The issuance of a patent is not conclusive as to its inventorship, scope, validity, or enforceability, and Boundless Bio’s patent rights may be challenged in the courts or patent offices in the United States and abroad. Boundless Bio may be subject to a third-party post-issuance submission of prior art to the USPTO challenging the validity of one or more claims of Boundless Bio’s patents or patents Boundless Bio may license in the future. Third-party submissions may also be made prior to a patent’s issuance, precluding the granting of a patent based on Boundless Bio’s pending patent application or patent application Boundless Bio may license in the future. A third party may also claim that Boundless Bio’s patent rights are invalid or unenforceable in a litigation. The outcome following legal assertions of invalidity and unenforceability is unpredictable. In addition, Boundless Bio may become involved in opposition, derivation, revocation, reexamination, reissue, post-grant, proceedings, inter partes review, interference proceedings, or other similar proceedings in the United States and/or foreign jurisdictions challenging Boundless Bio’s patent rights. An adverse determination in any such submission, proceeding, or litigation could reduce the scope of, or invalidate or render unenforceable, Boundless Bio’s patent rights, and may allow third parties, including generic drug companies, to commercialize its ecDTx and other proprietary technologies Boundless Bio may develop and compete directly with Boundless Bio.

Moreover, some of Boundless Bio’s patent rights may in the future be co-owned with third parties. In the United States, each co-owner has the freedom to license and exploit the technology. If Boundless Bio is unable to obtain an exclusive license to any such third-party co-owners’ interest in such patent rights, such co-owners may be able to license their rights to other third parties, including Boundless Bio’s competitors, and Boundless Bio’s competitors could market competing products and technology. In addition, Boundless Bio may need the cooperation of any such co-owners of such patent rights in order to enforce such patent rights against third parties, and such cooperation may not be provided to Boundless Bio. Any of the foregoing could have a material adverse effect on Boundless Bio’s competitive position, business, financial conditions, results of operations, and prospects.

Boundless Bio may not be able to protect its intellectual property and proprietary rights throughout the world.

Filing, prosecuting, maintaining, enforcing, and defending patents on Boundless Bio’s ecDTx in all countries throughout the world is expensive, and the laws of foreign countries may not protect Boundless Bio’s intellectual property rights to the same extent as the laws of the United States. Prosecution of foreign patent applications is often a longer process and patents may grant at a later date, and with a shorter term, than in the United States. The requirements for patentability differ in certain jurisdictions and countries. Additionally, the patent laws of some countries do not afford intellectual property protection to the same extent as the laws of the United States. For example, other countries may impose substantial restrictions on the scope of claims, limiting patent protection to specifically disclosed embodiments. Consequently, Boundless Bio may not be able to prevent third parties from practicing its inventions in all countries outside the United States, or from selling or importing products made using its intellectual property in and into the United States or other jurisdictions. Competitors may use Boundless Bio’s intellectual property in jurisdictions where Boundless Bio has not pursued and obtained patent protection to develop their own products and, further, may export otherwise infringing products to territories where Boundless Bio has patent protection, but enforcement is not as strong as that in the United States. These products may compete with Boundless Bio’s products, and Boundless Bio’s patents or patents Boundless Bio may license in the future or other intellectual property rights may not be effective or sufficient to

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prevent them from competing. Many companies have encountered significant problems in protecting and defending intellectual property rights in foreign jurisdictions. The legal systems of certain countries, particularly certain developing countries, do not favor the enforcement of patents, trade secrets, and other intellectual property protection, particularly those relating to biopharmaceutical products, which could make it difficult for Boundless Bio to stop the infringement of its patents or marketing of competing products in violation of its intellectual property and proprietary rights generally. In addition, some jurisdictions, such as Europe, Japan, and China, may have a higher standard for patentability than in the United States, including, for example, the requirement of claims having literal support in the original patent filing and the limitation on using supporting data that is not in the original patent filing. Under those heightened patentability requirements, Boundless Bio may not be able to obtain sufficient patent protection in certain jurisdictions even though the same or similar patent protection can be secured in the United States and other jurisdictions.

Proceedings to enforce Boundless Bio’s intellectual property and proprietary rights in foreign jurisdictions could result in substantial costs and divert Boundless Bio’s efforts and attention from other aspects of its business, could put Boundless Bio’s patents and any patents Boundless Bio may license in the future at risk of being invalidated or interpreted narrowly, could put Boundless Bio’s patent applications and any patent applications Boundless Bio may license in the future at risk of not issuing, and could provoke third parties to assert claims against Boundless Bio. Boundless Bio may not prevail in any lawsuits that it initiates, and the damages or other remedies awarded, if any, may not be commercially meaningful. Accordingly, Boundless Bio’s efforts to enforce its intellectual property and proprietary rights around the world may be inadequate to obtain a significant commercial advantage from the intellectual property that Boundless Bio develops.

Many countries have compulsory licensing laws under which a patent owner may be compelled to grant licenses to third parties. In addition, many countries limit the enforceability of patents against government agencies or government contractors. In these countries, the patent owner may have limited remedies, which could materially diminish the value of such patent. If Boundless Bio is forced to grant a license to third parties with respect to any patents relevant to its business, its competitive position may be impaired, and its business, financial condition, results of operations, and prospects may be adversely affected. In addition, geopolitical actions in the United States and in foreign countries (such as the geopolitical conflicts in and around Ukraine and the Middle East; retaliatory measures by foreign countries in response to actions by the U.S., in particular, tariffs) could increase the uncertainties and costs surrounding the prosecution or maintenance of Boundless Bio’s patent applications or those of any future licensors and the maintenance, enforcement, or defense of its issued patents, which could impair its competitive intellectual property position. Many foreign countries could threaten to impose retaliatory measures that may adversely impact Boundless Bio’s intellectual property rights in those countries. For example, government actions may prevent filing, prosecution, and maintenance of issued patents in various jurisdictions experiencing geopolitical conflict. These actions could result in abandonment or lapse of Boundless Bio’s patents or patent applications, resulting in partial or complete loss of patent rights in such jurisdictions. In addition, jurisdictions outside of the U.S. could also permit Boundless Bio’s patents to be exploited without consent or compensation. For example, on March 14, 2025, Brazil enacted Law No. 15.122/2025 (known as the Economic Reciprocity Law), which provides a framework that allows for the suspension of obligations related to foreign entity’s intellectual property rights. In such circumstances Boundless Bio would not be able to prevent third parties from practicing its inventions or from selling or importing products made using its inventions in and into such jurisdictions. Accordingly, its competitive position may be impaired, and its business, financial condition, results of operations and prospects may be adversely affected.

Obtaining and maintaining Boundless Bio’s patent protection depends on compliance with various procedural, document submission, fee payment, and other requirements imposed by government patent agencies, and its patent protection could be reduced or eliminated for non-compliance with these requirements.