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 withlocal regulations) at screening.

• Histologically or cytologically confirmed adenocarcinoma of the prostate withoutsmall cell features.

• Metastatic disease in bone documented on bone scan, or in soft tissue documented onCT/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 onCT/MRI scan.

• Progressive disease in the setting of medical or surgical castration.

• Prior to randomization, there must be resolution of acute effects of any priortherapy to either baseline severity or CTCAE Grade ≤1.

• ECOG performance status 0 or 1, with a life expectancy of ≥12 months as assessed bythe investigator.

Exclusion Criteria:

• Any medical or psychiatric condition including recent (within the past year) oractive suicidal ideation/behavior or laboratory abnormality that may increase therisk of study participation or, in the investigator's judgment, make the participantinappropriate 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 cannothave received any cytotoxic chemotherapy with the following exceptions: Treatmentwith first-generation antiandrogen (ADT) agents and. Docetaxel treatment is allowedfor mCSPC.

• Previous administration with an investigational product (drug or vaccine) within 30days.

• Current use or anticipated need for drugs that are known strong CYP3A4/5 inhibitorsand inducers (with exception of enzalutamide as part of this study).

• Major surgery or palliative localized radiation therapy within 14 days beforerandomization.

• Inadequate organ function.