ESSA Pharma (NASDAQ:EPIX) plummeted about 70% premarket on Friday after ending its Phase 2 trial for a prostate cancer treatment.

The trial tested masofaniten with enzalutamide versus enzalutamide alone in patients with metastatic castration-resistant prostate cancer who had not yet used second-generation antiandrogens.

The decision followed an interim review of safety, PK, and efficacy data.

Results showed a higher PSA90 response rate in patients treated with enzalutamide alone than expected based on historical data.Additionally, no clear benefit was seen with the masofaniten-enzalutamide combination over enzalutamide alone.

A futility analysis showed a low likelihood of achieving the study’s primary endpoint. The combination was well-tolerated, with no new safety issues, matching the safety profile from Phase 1 studies.

ESSA also said it will end other clinical studies on masofaniten, both as a monotherapy and in combination with other treatments, to focus resources.