Sec Form 4 Filing - HEALY JAMES @ Y-mAbs Therapeutics, Inc. - 2025-09-16

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 HEALY JAMES 2. Issuer Name and Ticker or Trading Symbol Y-mAbs Therapeutics, Inc. [ YMAB] 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 SOFINNOVA INVESTMENTS INC., 3000 SAND HILL ROAD, BLDG. 4, SUITE 250 3. Date of Earliest Transaction (MM/DD/YY) 09/16/2025 (Street) MENLO PARK, CA94025 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 Common Stock 09/16/2025( 1 ) U 31,603 D $ 8.6 ( 2 ) 0 D Common Stock 09/16/2025( 1 ) D 25,080 ( 3 ) D 0 D Common Stock 09/16/2025( 1 ) U 2,194,278 D $ 8.6 ( 2 ) 0 I See footnote ( 5 )

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 Employee Stock Option (right to buy) $ 11.16 09/16/2025( 1 ) D 14,222 ( 6 ) 04/24/2028 Common Stock 14,222 ( 6 ) 0 D Employee Stock Option (right to buy) $ 21.45 09/16/2025( 1 ) D 8,000 ( 6 ) 06/12/2029 Common Stock 8,000 ( 6 ) 0 D Employee Stock Option (right to buy) $ 48.67 09/16/2025( 1 ) D 11,000 ( 6 ) 06/23/2030 Common Stock 11,000 ( 6 ) 0 D Employee Stock Option (right to buy) $ 37.53 09/16/2025( 1 ) D 11,000 ( 6 ) 06/10/2031 Common Stock 11,000 ( 6 ) 0 D Employee Stock Option (right to buy) $ 16.64 09/16/2025( 1 ) D 16,000 ( 6 ) 07/15/2032 Common Stock 16,000 ( 6 ) 0 D Employee Stock Option (right to buy) $ 8.13 09/16/2025( 1 ) D 13,950 ( 6 ) 06/08/2033 Common Stock 13,950 ( 6 ) 0 D Employee Stock Option (right to buy) $ 12.01 09/16/2025( 1 ) D 14,545 ( 6 ) 06/11/2034 Common Stock 14,545 ( 6 ) 0 D Employee Stock Option (right to buy) $ 4.51 09/16/2025( 1 ) D 33,450 ( 6 ) 06/30/2035 Common Stock 33,450 ( 6 ) 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other HEALY JAMES C/O SOFINNOVA INVESTMENTS INC. 3000 SAND HILL ROAD, BLDG. 4, SUITE 250 MENLO PARK, CA94025 X Signatures /s/ John LaRocca, Attorney-in-Fact 09/18/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Pursuant to the Agreement and Plan of Merger (the "Merger Agreement"), dated as of August 4, 2025, by and among Y-mAbs Therapeutics, Inc. (the "Issuer"), Yosemite Merger Sub, Inc. ("Purchaser"), Perseus BidCo US, Inc., a Delaware corporation ("Parent"), and Stark International Lux, a Luxembourg private limited liability company ("Ultimate Parent"), on September 16, 2025, Purchaser completed a tender offer for shares of common stock of the Issuer (each, a "Share") and thereafter merged with and into the Issuer, with the Issuer continuing as the surviving corporation and an indirect wholly owned subsidiary of Parent (the "Merger"). ( 2 )Pursuant to the terms of the Merger Agreement, the Shares were tendered at the Offer Acceptance Time (as defined in the Merger Agreement) in exchange for the right to receive $8.60 per Share, in cash, without interest, subject to any applicable withholding of taxes (the "Merger Consideration"). At the effective time of the Merger (being such date and at such time as the certificate of merger in respect of the Merger was duly filed with the Secretary of State of the State of Delaware in accordance with the DGCL) (the "Effective Time"), each issued and outstanding Share was cancelled in exchange for the Merger Consideration. ( 3 )Represents restricted stock units ("RSUs") granted to the Reporting Person pursuant to the Issuer's 2018 Equity Incentive Plan. Each RSU represents a contingent right to receive one share of Common Stock on the vesting dates of the RSU. ( 4 )At the Effective Time, pursuant to the Merger Agreement, each RSU award outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of (a) the total number of Shares issuable in settlement of such RSU award immediately prior to the Effective Time, multiplied by (b) the Merger Consideration. ( 5 )The Reporting Person is one of the managing members of the general partner of Sofinnova Management X-A, L.L.C., the general partner of Sofinnova Management X, L.P., the general partner of Sofinnova Venture Partners X, L.P., which directly holds the reported securities, and, as such, may be deemed to share voting and investment power over such shares. The Reporting Person disclaims beneficial ownership of the reported securities, except to the extent of his proportionate pecuniary interest in Sofinnova Ventures Partners X, L.P. ( 6 )At the Effective Time, pursuant to the Merger Agreement, each stock option ("Option") outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive cash, without interest, equal to the product of (a) the total number of Shares subject to such Option immediately prior to the Effective Time, multiplied by (b) the excess of the Merger Consideration over the exercise price payable per Share under such Option. Any Options with an exercise price equal to or in excess of the Merger Consideration were cancelled for no consideration.

Remarks: The foregoing descriptions in the footnotes to this Form 4 are qualified in their entirety by reference to the terms of the Merger Agreement. In the event of any conflict between the descriptions above and the terms set forth in the Merger Agreement, the terms set forth in the Merger Agreement shall control.

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