On Thursday, ESSA Pharma Inc. ( EPIX ) announced its plans to terminate the Phase 2 trial of masofaniten combined with enzalutamide versus enzalutamide single agent in patients with metastatic castration-resistant prostate cancer (mCRPC) naïve to second-generation antiandrogens.

This decision was based on a protocol-specified interim review of the safety, PK, and efficacy data, which showed a much higher rate of PSA90 response in patients treated with Pfizer Inc’s Xtandi (enzalutamide) monotherapy (which is the standard of care for this patient population) than expected based on historical data.

In addition, there was no clear efficacy benefit seen with the combination of masofaniten plus enzalutamide compared to enzalutamide single agent.

A futility analysis determined a low likelihood of meeting the prespecified primary endpoint of the study.

The combination of masofaniten plus enzalutamide was well-tolerated with no new safety signals and a safety profile similar to that seen in Phase 1 studies.

“We made the difficult decision to terminate this Phase 2 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,” said David Parkinson, President, and CEO.

As part of the effort to focus its resources, ESSA is also planning to terminate the other remaining company-sponsored and investigator-sponsored clinical studies evaluating masofaniten either as a monotherapy or in combination with other agents.

As of September 30, 2024, the company had available cash reserves and short-term investments of $126.8 million and net working capital of $124.3 million.

In September, ESSA Pharma ( EPIX ) announced the presentation of updated dose escalation data from its Phase 1/2 study of masofaniten (formerly EPI-7386) in combination with enzalutamide at the 2024 European Society for Medical Oncology (ESMO) Congress.

Across all dose cohorts, 88% of patients (14 of 16) achieved PSA50, 88% of patients (14 of 16) achieved PSA90, 69% of patients (11 of 16) achieved PSA90 in less than 90 days, and 63% of patients (10 of 16) achieved PSA