Relay Therapeutics’ RLY-2608 Shows Promising 11-Month PFS in Breast Cancer

On Monday, Relay Therapeutics Inc. (NASDAQ:RLAY) announced updated interim clinical data for RLY-2608, which is the company’s investigational allosteric, pan-mutant, and isoform-selective inhibitor of PI3Kα. Presented at the ASCO 2025 Annual Meeting, the data, with a median follow-up of 12.5 months, remained consistent with findings shared earlier in December 2024.

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The study showed a median progression-free survival/PFS of 11 months in second-line (2L) patients with PI3Kα-mutated, HR+, HER2- locally advanced or metastatic breast cancer who received RLY-2608 at 600mg twice daily/BI in combination with fulvestrant. The overall median PFS across all patients was 10.3 months. For the 52 patients who received the recommended Phase 3 dose (RP3D) and did not have a PTEN or AKT co-mutation, the median PFS was 18.4 months for those with kinase mutations and 8.5 months for those with non-kinase mutations.

The clinical benefit rate was 67% across all evaluable patients, with 39% achieving a confirmed objective response rate among those with measurable disease. Notably, 81% of patients experienced tumor reductions. RLY-2608 showed a well-differentiated tolerability profile, with mostly low-grade treatment-related adverse events (TRAEs) that were manageable. A 92% median dose intensity was maintained, and only two patients discontinued treatment due to TRAEs.

Relay Therapeutics plans to initiate the pivotal Phase 3 ReDiscover-2 (NCT06982521) study of RLY-2608 + fulvestrant in mid-2025. Additionally, dose escalation is ongoing for next-gen triplet combinations of RLY-2608 with atirmociclib (Pfizer’s CDK4-selective inhibitor) and ribociclib in front-line breast cancer regimens.

Relay Therapeutics Inc. (NASDAQ:RLAY) operates as a clinical-stage precision medicines company. It transforms the drug discovery process by enhancing small-molecule therapeutic discovery in targeted oncology and genetic disease indications.

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Disclosure: None. This article is originally published at Insider Monkey.