A Study of ARV-766 Given by Mouth in Men With Metastatic Prostate Cancer

Inclusion Criteria: Part A,B,C and D: * Histological, pathological, or cytological confirmed diagnosis of adenocarcinoma of the prostate. * Ongoing androgen deprivation therapy (ADT) with a gonadotropin releasing hormone analog or inhibitor, or orchiectomy (surgical or medical castration). * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 Part A: * Progression on at least 2 prior approved systemic therapies for metastatic prostate cancer (at least one must be a second-generation androgen inhibitor, e.g., abiraterone, enzalutamide, darolutamide, apalutamide). * Progressive mCRPC Part B: * Participants must have received at least one but no more than three prior second generation anti-androgen agents (e.g., enzalutamide or abiraterone). * Participants must have received no more than two prior chemotherapy regimens. * Progressive mCRPC Part C \& D: • Metastatic castration resistant or sensitive prostate cancer with radiographic evidence of metastatic disease Exclusion Criteria: Part A and B: * Known symptomatic brain metastases requiring steroids (above physiologic replacement doses). * Active inflammatory gastrointestinal disease, chronic diarrhea, known diverticular disease, or previous gastric resection or lap band surgery. * Radiation therapy within 4 weeks of first dose of study drug or prior irradiation to \>25% of the bone marrow. * Receipt of an investigational drug(s) within 4 weeks prior to anticipated first dose * Systemic anti-cancer therapy within 2 weeks of first dose of study drug (except agents to maintain castrate status). For bicalutamide, mitomycin C, or nitrosoureas the exclusion period must be 6 weeks and for abiraterone 4 weeks. Part C and D • Prior treatment with a second generation NHA