A Study to Learn How PF-06821497 (Mevrometostat) Works in Men With Metastatic Castration-resistant Prostate Cancer.

Inclusion Criteria

• Male participants aged ≥18 years (or the minimum age of consent in accordance with local regulations) at screening.
• Histologically or cytologically confirmed adenocarcinoma of the prostate without small cell features.
• Metastatic disease in bone documented on bone scan, or in soft tissue documented on CT/MRI scan.
• Surgically or medically castrated, with serum testosterone ≤50 ng/dL (≤1.73 nmol/L) at screening.
• Metastatic disease in bone documented on bone scan, or in soft tissue documented on CT/MRI scan.
• Progressive disease in the setting of medical or surgical castration.
• Prior to randomization, there must be resolution of acute effects of any prior therapy to either baseline severity or CTCAE Grade ≤1.
• ECOG performance status 0 or 1, with a life expectancy of ≥12 months as assessed by the investigator.

Exclusion Criteria

• Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
• Clinically significant cardiovascular disease.
• Known or suspected brain metastasis or active leptomeningeal disease.
• Participants must be treatment naïve at the mCRPC stage, eg, participants cannot have received any cytotoxic chemotherapy with the following exceptions: Treatment with first-generation antiandrogen (ADT) agents and. Docetaxel treatment is allowed for mCSPC.
• Previous administration with an investigational product (drug or vaccine) within 30 days.
• Current use or anticipated need for drugs that are known strong CYP3A4/5 inhibitors and inducers (with exception of enzalutamide as part of this study).
• Major surgery or palliative localized radiation therapy within 14 days before randomization.
• Inadequate organ function.