Relay Therapeutics, Inc. (RLAY) delivered encouraging news on Friday, sharing subset analyses from interim clinical data for its precision breast cancer drug zovegalisib (RLY-2608). The data, presented at the 2025 San Antonio Breast Cancer Symposium, showed the drug working effectively across a broad range of patients with PI3Kα-mutated, HR+/HER2- metastatic breast cancer.
Here's what makes this interesting: the drug demonstrated activity regardless of whether patients had previously been treated with fulvestrant or other selective estrogen receptor degraders (SERDs), and it didn't matter if patients had ESR1 mutations. That kind of consistency across different patient populations is exactly what you want to see in a precision medicine.
What the Numbers Show
As of the October 15, 2025 data cutoff, 118 patients had enrolled in the zovegalisib plus fulvestrant arm of the ReDiscover study. The efficacy analysis focused on 52 patients who received the 600mg twice-daily fasted dose and didn't have PTEN or AKT co-mutations. The median follow-up period was 20.2 months.
The median progression-free survival came in at 10.3 months for all patients. Among the 31 patients with measurable disease, the objective response rate hit 39%. For second-line patients specifically, the numbers looked even better: median PFS of 11.4 months and an ORR of 47%.
The drug also held up well in challenging patient groups. For patients who had already received prior SERD treatment, median PFS was 11.4 months with an ORR of 44% (7 out of 16 patients). And for patients who had a detectable ESR1 mutation at baseline, median PFS was 8.8 months with an impressive 60% ORR (6 out of 10 patients).
On the safety front, the tolerability profile remained consistent with what you'd expect from mutant-selective PI3Kα inhibition. Treatment-related adverse events were primarily low-grade, manageable, and reversible.
What Happens Next
Relay Therapeutics has several trials moving forward. The company is continuing enrollment in its Phase 3 ReDiscover-2 trial of zovegalisib plus fulvestrant in PI3Kα-mutated, CDK4/6 pre-treated, HR+/HER2- advanced breast cancer.
They're also advancing dose escalation in the Phase 1/2 ReDiscover trial, testing triplet combinations that could inform a future frontline metastatic trial. Additionally, enrollment continues in the Phase 1/2 ReInspire clinical trial evaluating the drug in vascular malformations.
Wells Fargo took notice of the progress, upgrading Relay Therapeutics from Equal-Weight to Overweight and more than doubling their price target from $6 to $13.
The Bigger Picture
Zovegalisib represents the lead program in Relay's efforts to develop mutant selective inhibitors of PI3Kα, which happens to be the most frequently mutated kinase in all cancers and all vascular malformations. If approved, the drug could potentially address nearly 500,000 patients in the United States, making it one of the largest patient populations for a precision medicine.
"Data presented today demonstrate the robust activity of zovegalisib + fulvestrant across subgroups of patients whose baseline characteristics are known to affect outcomes, such as prior fulvestrant or SERD and ESR1 mutation status," said Don Bergstrom, M.D., Ph.D., President of R&D at Relay Therapeutics.
"The broad range of activity highlights the importance of selectively targeting the driver of disease, mutant PI3Kα, and gives us confidence that the data observed to date should translate to our ongoing Phase 3 trial, ReDiscover-2."
Relay Therapeutics shares were up 3.21% at $8.03 at the time of publication on Friday. The stock is trading near its 52-week high of $8.36.
