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 masofaniten.
The open-label, two-arm, 2:1 randomized study aimed 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 at least one post-baseline prostate-specific antigen (PSA) measurement, and 41 patients had completed a minimum of three months of follow-up.
Lack of Efficacy and Futility Analysis
The primary endpoint of the trial was the proportion of patients achieving a PSA90 response. Secondary endpoints included additional PSA-based measures. However, the time-to-event parameters had not yet matured at the time of the interim analysis. The data indicated no clear efficacy benefit from the combination of masofaniten and enzalutamide. A futility analysis further suggested a low likelihood of meeting the prespecified primary endpoint.
Management's Perspective
"We designed this randomised study to rigorously evaluate the clinical benefit of adding masofaniten to enzalutamide," stated David Parkinson, president and CEO of ESSA Pharma. "We made the difficult decision to terminate this Phase II study following the interim analysis because we concluded that the emerging efficacy profile of masofaniten combined with enzalutamide would not likely meet the primary endpoint of the study, nor our internal requirements for a prostate cancer therapy candidate."
Masofaniten and mCRPC
Masofaniten (formerly EPI-7386) is an investigational oral, small-molecule androgen receptor (AR) inhibitor. The trial's design sought to improve outcomes for mCRPC patients, a population facing limited treatment options after initial therapies fail. The discontinuation of this trial represents a setback in the ongoing efforts to develop more effective treatments for this advanced stage of prostate cancer.
Safety Profile
Despite the termination, the combination of masofaniten and enzalutamide demonstrated a favorable safety profile, consistent with previous Phase I studies. This suggests that while the drug combination may not provide the desired efficacy, it does not introduce significant new safety concerns.
