Washington, D.C. 20549




Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.   )


Filed by the Registrant  x
Filed by a Party other than the Registrant  ¨
Check the appropriate box:
¨ Preliminary Proxy Statement
¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
¨ Definitive Proxy Statement
x Definitive Additional Materials
¨ Soliciting Material under §240.14a-12
Y-mAbs Therapeutics, Inc.
(Name of Registrant as Specified In Its Charter)
(Name of Person(s) Filing Proxy Statement, if other than the Registrant)
Payment of Filing Fee (Check the appropriate box):
x No fee required.
¨ Fee paid previously with preliminary materials.
¨ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a6(i)(1) and 0-11





Get informed before you vote *If you choose to vote these shares in person at the meeting, you must request a “legal proxy.” To do so, please follow the instructions at www.ProxyVote.com or request a paper copy of the materials, which will contain the appropriate instructions. Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number Your Vote Counts! FLASHID-JOB# For complete information and to vote, visit www.ProxyVote.com Control # Ricky Campana P.O. Box 123456 Suite 500 51 Mercedes Way Edgewood, NY 11717 1 OF 2 322,224 148,294 30# Hextone, Inc. P.O. Box 9142 Farmingdale, NY 11735 XXXX XXXX XXXX XXXX Y-MABS THERAPEUTICS, INC. 2022 Annual Meeting Vote by June 08, 2022 11:59 PM ET You invested in Y-MABS THERAPEUTICS, INC. and it's time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the shareholder meeting to be held on June 09, 2022. View the Form 10-K, Notice & Proxy Statement online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 26, 2022. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to [email protected]. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. Vote in Person at the Meeting* June 09, 2022 10:00 AM EDT Y-mAbs Therapeutics, Inc. via the internet at https://web.lumiagm.com/257688918 password: ymabs2022


Voting Items Board Recommends THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming shareholder meeting. Please follow the instructions on the reverse side to vote these important matters. Vote at www.ProxyVote.com FLASHID-JOB# Control # XXXX XXXX XXXX XXXX 1.00000 322,224 148,294 Under New York Stock Exchange rules, brokers may vote “routine” matters at their discretion if your voting instructions are not communicated to us at least 10 days before the meeting. We will nevertheless follow your instructions, even if the broker’s discretionary vote has already been given, provided your instructions are received prior to the meeting date. Y-MABS THERAPEUTICS, INC. 2022 Annual Meeting Vote by June 08, 2022 11:59 PM ET 1. Election of Directors Nominees: 01 Dr. Gérard Ber 02 David N. Gill For 2. To ratify the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2022. For 3. To approve, on a non-binding advisory vote basis, the compensation of the Company's named executive officers. For NOTE: The transaction of any other business that may properly come before the Annual Meeting or any adjournment or postponement thereof.