Relay Therapeutics touted positive interim progression-free survival data for its PI3Kα inhibitor in heavily treated breast cancer patients.
In the early-stage ReDiscover trial, Relay is investigating RLY-2608 in four arms: one as a monotherapy, one in combination with fulvestrant, a third with fulvestrant plus Pfizer’s CDK4 inhibitor atirmociclib, and the fourth testing RLY-2608 with fulvestrant and ribociclib, the current standard of care.
According to the biotech’s release on Monday, patients with HR-positive, HER2-negative locally advanced or metastatic breast cancer who received 600 mg of RLY-2608 plus fulvestrant showed “clinically meaningful” PFS.
Relay’s stock $RLAY was up about 5% in premarket trading on Monday.
Among the 52 patients who took that dose of Relay’s inhibitor, the median PFS was 9.2 months across all mutations and 10.3 months among patients with kinase mutations, while 57% of patients saw a clinical benefit. In 30 patients with measurable disease, one-third of patients had a partial response, earning a 33% objective response rate, and 73% of patients saw reductions in tumors. In 15 patients who had a kinase mutation, there was a 53% overall response rate.
Don Bergstrom“These interim data suggest that by selectively targeting mutant PI3Kα, RLY-2608 has the potential to offer a level of benefit to patients that has not previously been possible with existing non-selective medicines, while also having significantly less toxicity,” Relay R&D president Don Bergstrom said in a statement.
As for safety, there were mostly low-grade, treatment-related adverse events. Only two patients discontinued treatment because of adverse events. One-fourth of patients experienced a grade 3 treatment-related event.
Bergstrom said Relay will “move quickly” to share the data with regulators and design a pivotal study that the company hopes to start next year.
Other arms of the study are still ongoing. The arm testing RLY-2608 plus ribociclib and fulvestrant is on track to identify a dose of Relay’s drug that can be safely combined with a full dose of ribociclib. Initial safety data are expected before the end of the year.
Relay had cash, cash equivalents and investments of $688 million as of the end of the second quarter, with enough runway to go into the second half of 2026.