Medivation (MDVN) announced on Tuesday morning that the Phase III PREVAIL study, testing Xtandi (enzalutamide) in chemotherapy-naive patients with advanced prostate cancer, was stopped early after meeting both co-primary endpoints of Overall Survival (OS) and Radiographic Progression-Free Survival (rPFS). An independent data monitoring committee recommended that patients receiving placebo immediately begin receiving active drug. The PREVAIL study is a global trial of enzalutamide in 1,715 men with metastatic prostate cancer that have progressed despite androgen deprivation therapy, and who had not yet received chemotherapy. Despite the apparent success in the PREVAIL study, shares of Medivation sold off with the market open.
Xtandi was approved by the FDA in August of 2012 for metastatic castration-resistant prostate cancer (mCRPC) previously treated with docetaxel. An approval in chemo-naive disease would expand the market opportunity significantly. The company expects to begin the regulatory process early next year.
A competing drug from Johnson & Johnson (JNJ), Zytiga, was approved in chemo-naive disease in December of last year. Sales in 2011 vs. 2012 of $301M and $961M, respectively, don’t account for approval in pre-chemo metastatic castration resistant prostate cancer. For the 6 months ended June 30, 2013, Johnson and Johnson reported $739M in Zytiga sales, demonstrating increased momentum in the broader cancer indication. The consensus on the street is that Zytiga sales will continue to grow at this rate to reach $1.8 billion by 2015.
In the study, patients treated with Xtandi demonstrated a statistically significant overall survival benefit when compared to patients receiving placebo (p < 0.0001). Xtandi also provided a 30% reduction in risk of death compared with placebo (Hazard Ratio=0.70; 95% confidence interval, 0.59-0.83). By comparison, Zytiga generated a mOS of 35.3 months with a hazard ratio of 0.79, a 21% reduction in risk of death compared to placebo. Placebo arms of these trials performed quite similarly. Further, Xtandi-treated patients showed a statistically significant radiographic progression-free survival (rPFS) advantage compared with patients receiving placebo (p < 0.0001). Xtandi provided an 81% reduction in risk of progression or death compared with placebo (Hazard Ratio=0.19; 95% confidence interval, 0.15-0.23).
MDVN jumped 10% in the pre-market on Tuesday before trading off, in-part because this was not entirely unexpected, but also because some analysts have focused (inappropriately in our view) on median overall survival as opposed to hazard ratios. At mid-day MDVN traded at $50.92, a 2% gain on the previous close. Now, it seems success comes down to marketing. We remain bullish on MDVN.