Relay Therapeutics has beaten its survival goal in a first-in-human breast cancer study, positioning the biotech to move into a pivotal trial that could establish its candidate as a challenger to AstraZeneca’s Truqap.
Ahead of the readout, Relay identified the 5.5-month progression-free survival (PFS) seen in a study of AstraZeneca’s Truqap as the benchmark for its trial. Monday, Relay reported a median PFS of 9.2 months in patients who received its PI3Kα inhibitor RLY-2608 in an early-phase trial. The biotech plans to start a pivotal study in 2025.
Relay saw the PFS duration in 64 patients who received its recommended phase 2 dose in combination with Pfizer’s Faslodex. All patients had received at least one endocrine therapy and one CDK4/6 inhibitor, leading Relay to use a subgroup of the Truqap study as its benchmark. AstraZeneca didn’t limit enrollment in its trial to participants who had received a CDK4/6 inhibitor.
Cross-trial comparisons can be unreliable, but the almost four-month difference between the PFS reported in the RLY-2608 and Truqap trials has encouraged Relay to advance its candidate. Talking at a Goldman Sachs event in June, Donald Bergstrom, M.D., Ph.D., president of R&D at Relay, said Truqap is the most likely comparator for a potential pivotal trial of RLY-2608.
Peter Rahmer, Relay’s chief corporate development officer, added that he expected the RLY-2608 data to “be quite interpretable” against the benchmark set by Truqap. Rahmer said a “6-month PFS landmark analysis rate decently north of 50%” would give Relay confidence RLY-2608 could beat Truqap in a head-to-head study. Relay reported six and nine-month PFS of 64.1% and 60.1%, respectively.
Truqap currently competes with Novartis’ Piqray for the market. The rate of grade 3 hyperglycemia is a factor that informs choices between the drugs. Seven of the 355 recipients of Truqap in a phase 3 trial had grade 3 hyperglycemia, resulting in a frequency of 2%. One-third of patients in a Piqray study had (PDF) a grade 3 or worse reaction.
Relay reported one case of grade 3 hyperglycemia at its recommended phase 2 dose, suggesting its drug candidate could perform at least as well as Truqap on that front. Two patients discontinued treatment because of adverse events, one for grade 1 itching and one for grade 1 nausea and fatigue.
Boosted by the data, Relay plans to start a pivotal trial of RLY-2608 in second-line patients next year. The biotech is also planning to advance work on triple combinations, which add Pfizer’s atirmociclib or Novartis’ Kisqali to the mix. Relay, which is seeking a partner for lirafugratinib after talking to the FDA, expects its cash runway to extend into the second half of 2026.
Editor's note: This story was updated at 8 am on Sept. 9 to include data from Relay’s presentation.