Relay Therapeutics' Zovegalisib Shows Promising Phase 1/2 Data in Metastatic Breast Cancer — Relay Therapeutics, Inc.

Event summary

Relay Therapeutics presented Phase 1/2 data for zovegalisib + fulvestrant at ESMO TAT Congress 2026, showing 11.1-month median PFS in heavily pre-treated PI3Kα-mutated, HR+/HER2- metastatic breast cancer patients.
The 400mg BID fed dose demonstrated similar efficacy to the 600mg BID fasted dose, with median PFS of 11.2 months for kinase mutations and 11.0 months for non-kinase mutations.
Zovegalisib + fulvestrant maintained a favorable tolerability profile, with low-grade, manageable, and reversible treatment-related adverse events.
The Phase 3 ReDiscover-2 trial, initiated mid-2025, is evaluating zovegalisib 400mg BID + fulvestrant versus capivasertib + fulvestrant in PI3Kα-mutated, HR+/HER2- advanced breast cancer patients.

The big picture

Relay Therapeutics' data presentation at ESMO TAT Congress 2026 underscores the growing focus on precision medicine in oncology, particularly targeting PI3Kα mutations in metastatic breast cancer. The company's mutant-selective approach aims to address limitations of traditional PI3Kα inhibitors, potentially offering a differentiated therapeutic option for a significant patient population. The ongoing Phase 3 trial will be critical in validating zovegalisib's clinical benefit and positioning it against competitors like capivasertib.

What we're watching

Clinical Validation: Whether the Phase 1/2 efficacy and safety data for zovegalisib + fulvestrant will translate into successful outcomes in the ongoing Phase 3 ReDiscover-2 trial.
Regulatory Pathway: The pace at which the FDA will review and potentially approve zovegalisib, given its Breakthrough Therapy designation for the Phase 3 trial population.
Market Differentiation: How Relay Therapeutics will position zovegalisib against existing PI3Kα inhibitors and other targeted therapies in the HR+/HER2- metastatic breast cancer space.