Sec Form 4 Filing - Yi Kathy @ Theseus Pharmaceuticals, Inc. - 2024-02-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Yi Kathy 2. Issuer Name and Ticker or Trading Symbol Theseus Pharmaceuticals, Inc. [ THRX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O THESEUS PHARMACEUTICALS, INC., 314 MAIN STREET 3. Date of Earliest Transaction (MM/DD/YY) 02/14/2024 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Stock Units ( 1 ) ( 2 ) 02/14/2024 D 3,250 ( 3 ) ( 3 ) Common Stock 3,250 ( 3 ) 0 D Stock Option (Right to Buy) $ 4.0347 02/14/2024 D 99,634 ( 4 ) ( 4 ) Common Stock 99,634 ( 4 ) 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Yi Kathy C/O THESEUS PHARMACEUTICALS, INC. 314 MAIN STREET CAMBRIDGE, MA02142 X Signatures /s/ Bradford Dahms, Attorney-in-Fact 02/14/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the terms of that certain Agreement and Plan of Merger (the "Merger Agreement"), dated as of December 22, 2023, by and among the Issuer, Concentra Biosciences, LLC, a Delaware limited liability company ("Parent") and Concentra Merger Sub II, Inc., a Delaware corporation and a wholly owned subsidiary of Parent ("Merger Sub"), Merger Sub completed a tender offer for shares of common stock of the Issuer (each, a "Share") and thereafter merged with and into the Issuer, effective as of February 14, 2024 (the "Effective Time") with the Issuer surviving the merger. ( 2 )Each Issuer restricted stock unit ("Issuer RSU") represents a contingent right to receive one Share. ( 3 )Pursuant to the terms of the Merger Agreement, each outstanding Issuer RSU that was outstanding and unvested immediately prior to the Effective Time vested in full. At the Effective Time, each Issuer RSU then outstanding was cancelled and converted into (i) a cash payment equal to the product of (A) the total number of Shares then underlying such Issuer RSU multiplied by (B) $4.05 per Share in cash (the "Cash Amount"), without interest and subject to any withholding of taxes; and (ii) one non-transferable contractual contingent value right per Share (each, a "CVR") subject to such Issuer RSU, which represents the right to receive potential payments, in cash, subject to any applicable tax withholding and without interest, all upon the terms and subject to the conditions as set forth in the Offer to Purchase, as amended, and in the related Letter of Transmittal. ( 4 )Pursuant to the terms of the Merger Agreement, immediately prior to the Effective Time, each outstanding and unvested option to purchase Shares granted under an Issuer equity plan (each, an "Issuer Stock Option") vested in full. Pursuant to the terms of the Merger Agreement, at the Effective Time, each Issuer Stock Option with an exercise price that is less than the Cash Amount was cancelled and converted into the right to receive (i) a cash payment equal to the product of (A) the excess, if any, of the Cash Amount over the exercise price payable per Share with respect to such Issuer Stock Option, multiplied by (B) the total number of Shares subject to such Issuer Stock Option immediately prior to the Effective Time and (ii) one CVR for each Share underlying such Issuer Stock Option.

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* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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