X0306 4 2022-04-04 0 0001290149 Sierra Oncology, Inc. SRRA 0001295674 Thomson Mary Christina C/O SIERRA ONCOLOGY, INC. 1820 GATEWAY DRIVE, SUITE 110 SAN MATEO CA 94404 0 1 0 0 General Counsel, CCO & Sec'y Common Stock 2022-04-04 4 M 0 2000 13.04 A 2000 D Common Stock 2022-04-04 4 S 0 2000 35.1384 D 0 D Stock Option (Right to Buy) 13.04 2022-04-04 4 M 0 2000 0.00 A 2030-07-28 Common Stock 2000 0 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 22, 2020. The Reporting Person is subject to a Lock-Up Letter Agreement that expires on April 26, 2022. The sale of shares is a permissible exemption under the terms of the Lock-Up Letter Agreement. On July 28, 2021, the option vested as to 25% of the total shares granted on July 28, 2020, with the remaining shares from that grant vesting in equal monthly installments over the following 36 months, with 100% of the total shares vested on July 28, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date. /s/ Mary Christina Thomson 2022-04-04