RLAY · Relay Therapeutics, Inc.

This filing represents a pivotal clinical and strategic inflection point for Relay Therapeutics, shifting zovegalisib from late-line development toward a frontline Phase 3 program in a large, biomarker-defined breast cancer population. The 44% ORR in heavily pre-treated, median third-line patients — many with visceral disease, prior chemotherapy, and pre-diabetes — is clinically meaningful and directly compared in the press release to 53–55% ORR seen with current CDK4/6 inhibitor plus endocrine therapy doublets in first-line settings. Critically, the safety profile distinguishes this triplet: near-absence of Grade 3 hyperglycemia (0%) despite high pre-diabetes prevalence, low discontinuation (3%) and dose reduction (10%) rates for zovegalisib, and no febrile neutropenia — all suggesting a substantially improved therapeutic index over prior PI3Kα inhibitors like inavolisib, which carries >90% Grade 3+ AE rates in 1L. The pharmacokinetic synergy — atirmociclib boosting zovegalisib exposure ~2.5-fold without reciprocal impact — validates the mechanistic rationale for co-administration and informs the proposed 150mg BID Phase 3 dose. The planned Phase 3 trial design is robust: randomized, controlled against standard-of-care CDK4/6i + AI, enrolling frontline endocrine-sensitive patients with PIK3CA mutations, and powered for progression-free survival. Pfizer’s supply agreement de-risks execution by providing both atirmociclib and palbociclib, while Relay retains full global commercial rights and funding responsibility — preserving optionality and value capture. With Phase 3 initiation targeted for early 2027 and ongoing trials generating additional data (e.g., vascular anomalies at ISSVA 2026), this announcement materially advances zovegalisib’s path toward potential first-in-class, frontline approval in a $7–8B US TAM opportunity.