TMARCK: This study is comparing different treatments in people with metastatic castration-resistant prostate cancerA Phase 2/3, Randomized, Open-label, Study of MGC018 Versus Androgen Receptor Axis-targeted Therapy (Abiraterone or Enzalutamide) in Participants With Metastatic Castration-resistant Prostate Cancer

Exclusion

• Any underlying medical or psychiatric condition impairing participant's ability to receive, tolerate, or comply with the planned treatment or study procedures.
• Received >1 prior taxane-containing regimen for prostate cancer. A second taxane regimen of <60 days used as bridging for lutetium-177 is permitted.
• Received >3 total prior therapies for mCRPC
• Participants with known BRCA or ATM mutation (germline or somatic) are not eligible unless they received prior treatment with a PARP inhibitor where available, indicated and tolerated.
• Another hematologic or solid tumor ≥ stage 1 malignancy that completed surgery, last dose of radiotherapy, or last dose of systemic anti-cancer therapy ≤ 2 years from first dose of study treatment. Participants who had curative therapy for non-melanomatous skin cancer or for localized malignancy are eligible.
• Untreated, symptomatic central nervous system (CNS) metastasis.
• Prior treatment with any B7-H3 targeted agent for cancer,
• Contradictions to the use of corticosteroid treatment
• Prior stem cell, tissue, or solid organ transplant.
• Use of products that have published anti-prostate cancer activity or are known to decrease PSA.