ESSA Pharma has stopped its Phase II clinical trial evaluating masofaniten in combination with enzalutamide for patients with metastatic castration-resistant prostate cancer (mCRPC). The decision follows an interim analysis that revealed a higher-than-anticipated PSA90 response in patients receiving only enzalutamide, suggesting limited additional benefit from the masofaniten combination.
The Phase II trial was designed as an open-label, two-arm, 2:1 randomized study, aiming to enroll 120 patients across sites in the US, Canada, Australia, and France. At the time of the interim analysis, 52 patients had been enrolled, with 41 having completed at least three months of follow-up. The primary endpoint was the proportion of patients achieving a PSA90 response.
Interim Analysis and Futility
The interim review, conducted by ESSA Pharma's board of directors and senior management, indicated that the efficacy profile of masofaniten combined with enzalutamide was unlikely to meet the study's primary endpoint or the company's internal benchmarks for a viable prostate cancer therapy. A futility analysis further supported this conclusion, revealing a low probability of achieving the prespecified primary endpoint.
Masofaniten: An Investigational Androgen Receptor Inhibitor
Masofaniten, also known as EPI-7386, is an investigational oral, small-molecule androgen receptor (AR) inhibitor. The trial aimed to assess whether adding masofaniten to enzalutamide could improve outcomes for mCRPC patients compared to enzalutamide alone.
Safety and Tolerability
Despite the termination, the combination of masofaniten and enzalutamide demonstrated good tolerability, with a safety profile consistent with previous Phase I studies. However, the time-to-event parameters, including those related to PSA progression, had not yet matured at the time of the interim analysis.
Company Statement
ESSA Pharma's president and CEO, David Parkinson, stated that the decision to terminate the trial was difficult but necessary. He explained that the emerging efficacy profile of the combination did not justify continuing the study, given the primary endpoint and internal requirements for a prostate cancer therapy candidate. Parkinson expressed gratitude to the partners, investigators, employees, and, most importantly, the patients and their families involved in the clinical trials.
