Relay Therapeutics Reports Positive Early Results for Breast Cancer Drug

Relay Therapeutics has reported encouraging results from a small clinical trial of its experimental breast cancer drug, RLY-2608, which demonstrated a median progression-free survival of approximately nine months when combined with an older hormonal therapy. The results, which were released on Monday, led to a significant increase in Relay's stock value, boosting it by more than 50%.

In the study, RLY-2608 was administered alongside fulvestrant, a hormonal therapy, to 118 participants with locally advanced or metastatic breast cancer characterized by PI3Ka mutations. Of these, 64 patients received the recommended Phase 2 dose of RLY-2608. The drug regimen was particularly effective, shrinking tumors in nearly 75% of the 30 participants with measurable disease at the target dose. Ten of these participants showed a partial tumor response, indicating a substantial reduction in tumor size.

RLY-2608 targets the PI3Ka protein, a critical regulatory protein often implicated in the development of solid tumors due to mutations. Unlike other PI3Ka inhibitors, such as Novartis' Piqray and AstraZeneca's Truqap, which target the active site of the PI3Ka protein, Relay’s drug is designed to engage a different site. This approach is intended to reduce the toxicity often associated with existing PI3Ka inhibitors, which can lead to side effects like diarrhea, rash, and high blood sugar.

Relay's data suggest that RLY-2608 may indeed have a more favorable safety profile compared to existing treatments. In the trial, fewer patients experienced severe side effects, with only two out of the 64 at the target dose discontinuing treatment due to toxicity. The median progression-free survival of 9.2 months observed with RLY-2608 is also notably higher than the typical 5.5 months seen with current PI3Ka-targeting therapies.

Relay Therapeutics plans to advance RLY-2608 into a pivotal trial next year to further evaluate its efficacy and potential to replace existing treatment options for patients with metastatic breast cancer driven by PI3Ka mutations. Pending discussions with regulators, the company aims to compare the combination of RLY-2608 and fulvestrant against the current standard of care, which includes Truqap and fulvestrant. Relay is also exploring triplet drug combinations, which might be suitable for previously untreated patients, with more data expected later this year and pivotal trials anticipated to begin by 2026.

The positive trial results have placed Relay's market valuation back above $1 billion. In addition to its plans for RLY-2608, the company is seeking a commercialization partner for its most advanced drug candidate, which targets bile duct cancer.

Cover image credit: Doucefleur, iStock

Topics: Clinical Trials