X0206 3 2021-10-06 0 0001745020 Theseus Pharmaceuticals, Inc. THRX 0001787307 Dahms Bradford D. C/O THESEUS PHARMACEUTICALS, INC. 245 MAIN STREET CAMBRIDGE MA 02142 0 1 0 0 Chief Financial Officer Stock Option (right to buy) 4.0347 2031-05-26 Common Stock 332114 D Stock Option (right to buy) 9.9876 2031-08-26 Common Stock 23885 D The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period with 25% of the options vesting on May 25, 2022 and 1/48th of the options vesting monthly thereafter, subject to the Reporting Person's continuous service with the issuer The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period with 25% of the options vesting on August 27, 2022 and 1/48th of the options vesting monthly thereafter, subject to the Reporting Person's continuous service with the issuer. /s/ Bradford Dahms 2021-10-06