X0306 4 2021-04-15 0 0001808158 Repare Therapeutics Inc. RPTX 0001477123 Segal Lloyd Mitchell C/O REPARE THERAPEUTICS INC. 7210 FREDERICK-BANTING, SUITE 100 ST-LAURENT A8 H4S 2A1 QUEBEC, CANADA 0 1 0 0 President and CEO Common Stock 2021-04-15 4 S 0 5512 35.01 D 142954 I See Footnote Common Stock 5000 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 31, 2020. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $35.00 to $35.06, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote. These securities are registered in the name of Arvala Inc. (f/k/a 3996953 Canada Inc., the "Company"). The Reporting Person is the sole stockholder of the Company. /s/ Steve Forte, Attorney-in-Fact 2021-04-19