Essa's Shares Plunge After Dropping Prostate Cancer Drug

Essa Pharma is reevaluating its future plans after discontinuing the development of its prostate cancer drug, which did not succeed in a mid-stage clinical trial. The company's stock, trading under the symbol $EPIX, plummeted by up to 65% in premarket trading on Friday.

In a scheduled interim analysis of a Phase 2 study involving 52 patients with metastatic castration-resistant prostate cancer, Essa’s experimental drug masofaniten combined with Astellas and Pfizer’s Xtandi achieved a 64% response rate in the primary endpoint of PSA90, a measure of prostate-specific antigen levels. However, patients treated with Xtandi alone showed a higher response rate of 73%. The trial included participants who had not previously been treated with second-generation antiandrogens.

A futility analysis indicated that the trial was unlikely to meet its primary endpoint, according to the company. It was noted that single-agent Xtandi demonstrated a significantly higher PSA90 response rate than anticipated based on historical data, Essa revealed in a Thursday statement. Under a 2021 clinical collaboration and supply agreement, Astellas provided Xtandi for the Phase 2 trial.

Additionally, Essa Pharma, based in South San Francisco, is ceasing another early-stage study of masofaniten in combination with Johnson & Johnson’s Zytiga and Erleada in prostate cancer. The company will also terminate any investigator-sponsored trials, withdrawing all Investigational New Drug applications and clinical trial applications for masofaniten.

Essa Pharma announced that it is now dedicated to assessing its “strategic options.” As of the end of September, the company had $126.8 million in cash reserves and short-term investments.

Prostate cancer remains a particularly challenging area for drug development, with multiple companies, including MacroGenics and Exelixis, encountering significant difficulties in advancing their treatments through clinical trials this year.