Shares of Medivation (MDVN) traded off slightly on Wednesday morning (-4%) with the release of top-line results from the phase II TERRAIN trial, pitting Xtandi (enzalutamide) against Casodex (bicalutamide) in men with metastatic castration-resistant prostate cancer. The trial was, in fact, successful, with enzalutamide improving progression-free survival (PFS) meaningfully compared to bicalutamide, the leading anti-androgen drug on the market – a Hazard Ratio of 0.44 (95% Confidence Interval, 0.34-0.57; p < 0.0001). Median PFS was 15.7 months in the enzalutamide group compared to 5.8 months in the bicalutamide group.
Why the slump in share price? Investors weren’t thrilled with enzalutamide’s comparable safety. Serious adverse events were reported in 31.1% of enzalutamide-treated patients versus 23.3% of bicalutamide-treated patients. More specifically, Grade 3 or higher cardiac events occurred in 5.5% of enzalutamide-treated patients compared to just 2.1% of bicalutamide subjects, and two seizures were reported in the enzalutamide group versus 1 in the bicalutamide group. With nearly a 10-month PFS improvement, our view is that Wall Street may be taking a myopic view of the safety results.
TERRAIN involved patients with metastatic prostate cancer whose disease had progressed despite treatment with a luteinizing hormone-releasing hormone (LHRH) therapy, or following surgical castration, but prior to chemotherapy. Xtandi is already approved in prostate cancer, but TERRAIN was designed to move the drug further upstream in the clinic.
One or more of PropThink’s contributors are long MDVN.
