X0306 4 2022-03-18 0 0001290149 Sierra Oncology, Inc. SRRA 0001819688 Turner William D. C/O SIERRA ONCOLOGY, INC. 1820 GATEWAY DRIVE, SUITE 110 SAN MATEO CA 94404 0 1 0 0 Chief Reg & Tech Ops Officer Common Stock 2022-03-18 4 M 0 100 12.05 A 100 D Common Stock 2022-03-18 4 S 0 100 37.05 D 0 D Stock Option (Right to Buy) 12.05 2022-03-18 4 M 0 100 0.00 A 2030-08-04 Common Stock 100 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 March 19, 2021. 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 August 4, 2021, the option vested as to 25% of the total shares granted on August 4, 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 August 4, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date. /s/ Mary Christina Thomson, Attorney-In-Fact for William D. Turner 2022-03-22