Company: RPTX
Filing Date: 2025-11-17
Form Type: DEFA14A
Source: 0001193125-25-284040
Chunk: 0

Company: Repare Therapeutics Inc.
Filing Date: 2025-11-17
Form: DEFA14A
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-K CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): November 14, 2025 Repare Therapeutics Inc. (Exact Name of Registrant as Specified in Its Charter)

| Québec                       |     | 001-39335   |     | Not applicable     |
| (State or Other Jurisdiction 
 of Incorporation)            |     | -Commission 
 File Number |     | -I.R.S. Employer   
 Identification No. |

| 7171 Frederick-Banting, Building 2, Suite 270 
 St-Laurent, Québec, Canada                    |     | H4S 1Z9   |
| (Address of Principal Executive Offices)      |     | -Zip Code |

Registrant’s Telephone Number, Including Area Code: (857) 412-7018 Not Applicable (Former Name or Former Address, if Changed Since Last Report.) Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ☐ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |

| ☒ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 
 CFR 240.14a-12)                                                        |

| ☐ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |

| ☐ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

Securities registered pursuant to Section 12(b) of the Act:

| Title of each class         |     | Trading 
 Symbol  |     | Name of each exchange       
 on which registered         |
| Common shares, no par value |     | RPTX    |     | The Nasdaq Stock Market LLC |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2of the Securities Exchange Act of 1934 (§240.12b-2of this chapter).