On September 19, 2023, Mark A. Velleca, M.D., Ph.D., notified G1 Therapeutics, Inc. (the ?Company?) of his decision to resign from the Board of Directors (the ?Board?) of the Company effective as of September 30, 2023. Dr. Velleca was a member of the Board since May 2014. Dr. Velleca will continue to serve as a senior advisor to the Company pursuant to the terms of a Senior Advisor Agreement dated September 29, 2020 (the ?Agreement?), as amended by that certain First Amendment to Senior Advisor Agreement, dated as of September 20, 2023 (the ?Amendment?).