Clinical Trial Selected for Oral Presentation on Friday, October 8 at 3:15 p.m. ET

Preclinical Data Poster Presentation for RP-3500 Alone and in Combination with PARP Inhibitors

Company Virtual Webcast Event on Friday, October 8 at 5:00 p.m. ET

Repare Therapeutics Inc. (“Repare” or the “Company”) (Nasdaq: RPTX), a leading clinical-stage precision oncology company, today announced that it has been selected for an oral presentation of initial monotherapy clinical data from its ongoing Phase 1/2 clinical trial of RP-3500 and a poster presentation of preclinical data for RP-3500 at the upcoming AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics, being held October 7-10, 2021. In addition, the Company will be hosting a Virtual Investor Webcast Event on Friday, October 8, 2021 at 5:00 p.m. ET.

Oral Presentation Details on RP-3500 Early TRESR Monotherapy Trial Results:

Title: First-in-Human biomarker-driven phase I TRESR trial of ataxia telangiectasia and Rad3-related inhibitor (ATRi) RP-3500 in patients (pts) with advanced solid tumors harboring synthetic lethal (SL) genomic alterations

Presenter: Dr. Timothy Yap, MBBS, Ph.D., FRCP, Medical Director, Institute for Applied Cancer Science, Associate Professor, Department of Investigational Cancer Therapeutics, Division of Cancer Medicine, MD Anderson Cancer Center, Houston, Texas

Abstract Number: 4950

Session Title: Concurrent Session 04: Novel Precision Medicine Combination Trials

Date/Time: Friday, October 8, 2021 at 3:15 p.m. ET

Poster Presentation Details on Preclinical data for RP-3500 Alone and in Combination with PARP Inhibitors:

Title: RP-3500: A Novel, Potent and Selective ATR Inhibitor that is Effective in Pre-Clinical Models as a Monotherapy and in Combination with PARP Inhibitors

Presenter: Anne Roulston, Ph.D., Repare Therapeutics

Poster Number: P054

Date/Time: Thursday, October 7, 2021, at 9:00 a.m. ET

Company Virtual Investor Webcast Event Details:

The Company will host a virtual investor webcast on Friday, October 8, 2021 at 5:00 p.m. ET to further discuss the initial monotherapy RP-3500 data that will be presented at the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics. Repare’s executive management team will be joined by Dr. Timothy Yap, MBBS, Ph.D., FRCP, MD Anderson Cancer Center, Houston, Texas.

A live video webcast and presentation slides will be available on the Investor section of the Company’s website at https://ir.reparerx.com/news-and-events/events. A webcast replay will also be available for at least 30 days following the call.

About RP-3500

RP-3500 is a potent and selective oral small molecule inhibitor of ATR (Ataxia Telangiectasia and Rad3 related protein kinase) being developed for the treatment of solid tumors with specific genome instability related genomic alterations including those in the ATM (ataxia-telangiectasia mutated) gene.

About Repare Therapeutics’ SNIPRx® Platform

Repare’s SNIPRx® platform is a genome-wide CRISPR-based screening approach that utilizes proprietary isogenic cell lines to identify novel and known synthetic lethal gene pairs and the corresponding patients who are most likely to benefit from the Company’s therapies based on the genetic profile of their tumors. Repare’s platform enables the development of precision therapeutics in patients whose tumors contain one or more genomic alterations identified by SNIPRx® screening, in order to selectively target those tumors in patients most likely to achieve clinical benefit from resulting product candidates.

About Repare Therapeutics, Inc.

Repare Therapeutics is a leading clinical-stage precision oncology company enabled by its proprietary synthetic lethality approach to the discovery and development of novel therapeutics. The Company utilizes its genome-wide, CRISPR-enabled SNIPRx® platform to systematically discover and develop highly targeted cancer therapies focused on genomic instability, including DNA damage repair. The Company’s pipeline includes its lead product candidate, RP-3500, a potential leading ATR inhibitor currently in Phase 1/2 clinical development, its second clinical candidate, RP-6306, a PKMYT1 inhibitor currently in Phase 1 clinical development, a Polθ inhibitor program, as well as eight other early-stage, pre-clinical programs. For more information, please visit reparerx.com.

SNIPRx® is a registered trademark of Repare Therapeutics Inc.

Forward-Looking Statements

This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements in this press release other than statements of historical facts are “forward-looking statements. These statements may be identified by words such as “aims,” “anticipates,” “believes,” “could,” “estimates,” “expects,” “forecasts,” “goal,” “intends,” “may,” “plans,” “possible,” “potential,” “seeks,” “will” and variations of these words or similar expressions that are intended to identify forward-looking statements, although not all forward-looking statements contain these words. Forward-looking statements in this press release include, but are not limited to, statements regarding the clinical development of the Company’s lead product candidate, RP-3500 including details of the ongoing Phase 1/2 clinical trial of RP-3500 and the Company's plans for presentation of data relating to the clinical development program. These forward-looking statements are based on the Company’s expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties that could cause the Company’s clinical development programs, future results or performance to differ materially from those expressed or implied by the forward-looking statements. Many factors may cause differences between current expectations and actual results, including the impacts of the COVID-19 pandemic on the Company’s business, clinical trials and financial position, unexpected safety or efficacy data observed during preclinical studies or clinical trials, clinical trial site activation or enrollment rates that are lower than expected, changes in expected or existing competition, changes in the regulatory environment, the uncertainties and timing of the regulatory approval process, and unexpected litigation or other disputes. Other factors that may cause the Company’s actual results to differ from those expressed or implied in the forward-looking statements in this press release are identified in the section titled "Risk Factors" in the Company’s Quarterly Report for the period ended June 30, 2021 filed with the Securities and Exchange Commission (“SEC”) on August 12, 2021 and any subsequent filings with the SEC. The Company expressly disclaims any obligation to update any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise, except as otherwise required by law.

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