This Study Will Explore Whether a Combination of the Investigational Drug Mevrometostat (PF-06821497) and Enzalutamide Will Work Better Than Taking Enzalutamide Alone in Participants With mCSPC Who Are ARPI naïve.

This is a global, multicenter, randomized, double-blind, placebo-controlled Phase 3 study evaluating mevrometostat in combination with enzalutamide versus placebo in combination with enzalutamide in participants with mCSPC who have not received systemic anticancer treatments with the exception of androgen-deprivation therapy (ADT) and first-generation antiandrogen agents. Prior therapy with up to 3 months of ADT (chemical or surgical) is allowed, with no radiographic evidence of disease progression or rising PSA levels prior to Day 1. This study consists of a Screening Phase, Randomization, Treatment Phase, Safety Follow-up, and Long-Term Follow-up. Participants will be randomized on a 1:1 basis to receive (Arm A) mevrometostat (PF-06821497) in combination with enzalutamide, or (Arm B) placebo in combination with enzalutamide.