Sec Form 4 Filing - Gad Thomas @ Y-mAbs Therapeutics, Inc. - 2021-03-10

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 Gad Thomas 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 X __ Officer (give title below) _____ Other (specify below) See remarks (Last) (First) (Middle) C/O Y-MABS THERAPEUTICS, INC., 230 PARK AVENUE, SUITE 3350 3. Date of Earliest Transaction (MM/DD/YY) 03/10/2021 (Street) NEW YORK, NY10169 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 03/10/2021 J 1,029,927 A 1,625,927 I By GAD Enterprises LLC ( 2 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Gad T homas C/O Y-MABS THERAPEUTICS, INC. 230 PARK AVENUE, SUITE 3350 NEW YORK, NY10169 X See remarks Signatures /s/ THOMAS GAD 03/12/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )WG Biotech Aps transferred 1,029,927 shares of the Common Stock of Y-mAbs Therapeutics, Inc. (the "Company") to GAD Enterprises, LLC in exchange for 20,565 ordinary shares of WG Biotech ApS. The closing sale price of the Company's Common Stock on March 10, 2021, the date of the transaction, was $35.30. These shares were previously reported as beneficially owned by the Reporting Person based on such person's 18.70% ownership interest in WG Biotech ApS, which was exchanged for such shares pursuant to an exchange agreement. As a result, there is no change in the total shares beneficially owned by the Reporting Person, just a change in the indirect nature of such beneficial ownership interest. ( 2 )Reporting Person is sole member of GAD Enterprises, LLC and the sole member and manager of GAD Management, LLC, the manager of GAD Enterprises, LLC, and as such Reporting Person has sole voting and dispositive power with respect to such shares.

Remarks: Chairman, President and Head of Business Development & Strategy

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

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

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