Pfizer and Astellas said Thursday that a Phase III study evaluating Xtandi (enzalutamide) plus androgen deprivation therapy (ADT) versus ADT alone in patients with non-metastatic castration-resistant prostate cancer (CRPC) met its primary endpoint of improved metastasis-free survival (MFS). The companies noted that the drug is "the first androgen receptor-inhibitor to demonstrate a statistically significant improvement in [MFS] in this patient population in a randomised, controlled clinical trial."
The PROSPER trial randomised around 1400 patients with CRPC whose disease had progressed, based on a rising PSA level despite ADT, but who had no symptoms with no prior or present evidence of metastatic disease. The study investigated Xtandi at a dose of 160 mg taken orally once daily plus ADT, versus placebo plus ADT.
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According to the drugmakers, a preliminary safety analysis of the trial "appears consistent" with the safety profile of Xtandi in earlier studies. Pfizer and Astellas indicated that based on results of the study, they plan to discuss the data with global health authorities to potentially support expanding the label for Xtandi to cover all patients with CRPC.
Xtandi is currently approved for the treatment of metastatic CRPC based on clinical data from previous studies that showed a significant overall survival benefit for the drug versus placebo. Pfizer gained certain rights to Xtandi after agreeing to buy Medivation for around $14 billion last year, with the latter company having previously rebuffed Sanofi's takeover attempts.
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