Pfizer Inc. and Astellas Pharma Inc. announced the Phase 4 PLATO study, evaluating the efficacy and safety of continued treatment with XTANDI® (enzalutamide), plus abiraterone acetate and prednisone as compared to treatment with abiraterone acetate and prednisone alone, did not meet its primary endpoint of improvement in progression-free survival (PFS) in patients with chemotherapy-naïve metastatic castration-resistant prostate cancer (CRPC) whose prostate-specific antigen (PSA) has previously progressed on XTANDI. XTANDI is approved by the U.S. Food and Drug Administration for the treatment of patients with metastatic castrate-resistant prostate cancer (CRPC), based on clinical studies showing statistically significant overall survival benefit versus placebo. The Phase 4 PLATO trial (NCT01995513) is a global randomized, double-blind, placebo-controlled, two-period study designed to evaluate the efficacy and safety of continued treatment with XTANDI plus abiraterone acetate and prednisone at the time of confirmed PSA progression, as compared to treatment with abiraterone acetate and prednisone alone at the time of PSA progression. The study enrolled 509 patients with chemotherapy-naïve metastatic CRPC who received open label XTANDI during period 1 of the study, until PSA progression was confirmed. Eligible patients were then randomized to one of the two treatments and assessed for the primary endpoint of the study, PFS, defined by either: 1) radiographic progression or 2) unequivocal clinical progression or 3) death during the study. Period 1 patients were treated with XTANDI 160mg/day orally and period 2 patients were treated with blinded XTANDI 160 mg/day orally in combination with abiraterone at a dose of 1,000 mg/day administered orally and prednisone at a dose of 5 mg administered orally twice daily, versus placebo plus the same doses of abiraterone acetate and prednisone.