X0206 3 2018-09-20 0 0001722964 Y-mAbs Therapeutics, Inc. YMAB 0001752940 Kruse Bo C/O Y-MABS THERAPEUTICS, INC. 230 PARK AVE, 33RD FLOOR NEW YORK NY 10169 1 1 0 0 EVP, CFO, Secy & Treas. Common Stock 300000 D Common Stock 57077 I By Investeringsselskabet G.H. ApS Employee Stock Option (right to buy) 2.00 2025-06-10 Common Stock 300000 D Employee Stock Option (right to buy) 4.38 2026-10-21 Common Stock 133000 D Employee Stock Option (right to buy) 8.50 2026-12-14 Common Stock 14000 D Employee Stock Option (right to buy) 11.16 2028-04-24 Common Stock 75000 D Investeringsselskabet G.H. ApS is Reporting Person's personal holding company of which Reporting Person is the sole owner and as such has the sole voting and dispositive power with respect to such shares. The stock option vested and became exercisable as to 25% of the shares subject to the option on June 10, 2016, and thereafter vests as to 1/48th of the shares in equal monthly installments, until such time as the option is 100% vested, subject to the continuing employment of the Reporting Person on each vesting date. The stock option vested and became exercisable as to 25% of the shares subject to the option on October 21, 2017, and thereafter vests as to 1/48th of the shares in equal monthly installments, until such time as the option is 100% vested, subject to the continuing employment of the Reporting Person on each vesting date. The stock option vested and became exercisable as to 25% of the shares subject to the option on December 14, 2017, and thereafter vests as to 1/48th of the shares in equal monthly installments, until such time as the option is 100% vested, subject to the continuing employment of the Reporting Person on each vesting date. The stock option shall vest and become exercisable as to 25% of the shares subject to the option on April 24, 2019, and thereafter vests as to 1/48th of the shares in equal monthly installments, until such time as the option is 100% vested, subject to the continuing employment of the Reporting Person on each vesting date. /s/ Bo Kruse 2018-09-20