X0306 4 2021-06-03 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 2021-06-03 4 S 0 6648 31.74 D 126936 I See footnote Common Stock 2021-06-04 4 S 0 17180 30.64 D 109756 I See footnote Common Stock 2021-06-04 4 S 0 12172 31.36 D 97584 I See footnote Common Stock 2021-06-04 4 M 0 5000 1.637 A 10000 D Common Stock 2021-06-04 4 S 0 5000 31.25 D 5000 D Employee Stock Option (right to buy) 1.637 2021-06-04 4 M 0 5000 0.00 D 2027-06-22 Common Stock 5000 283683 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $31.50 to $32.15 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 footnotes (1), (3), (4) and (5). 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. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $30.20 to $31.19 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $31.215 to $31.65 inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $30.90 to $31.49 inclusive. Twenty-five percent (25%) of the shares subject to the option vested on June 22, 2018, and one thirty-sixth (1/36th) of the remaining shares subject to the option vested or shall vest each month thereafter, subject to Reporting Person continuing to provide service through each such date. /s/ Steve Forte, Attorney-in-Fact 2021-06-07