Testing the Addition of Immunotherapy With Hu5F9-G4 (Magrolimab) to the Usual PARP Inhibitor, Olaparib for Treatment of Metastatic or Recurrent Breast or Castrate-Resistant Prostate Cancer With BRCA Mutations

This phase I/Ib trial studies the side effects and best dose of Hu5F9-G4 (magrolimab) when given in combination with olaparib for the treatment of patients with breast or castrate-resistant prostate cancer that have spread from where they first started (primary site) to other places in the body (metastatic) or have come back after a period of improvement (recurrent) and have mutations in the BRCA1/2 genes. Magrolimab is a monoclonal antibody with potential anticancer activity and the cability to stimulate the immune system and may interfere with the ability of tumor cells to grow and spread. A monoclonal antibody is a type of protein that can bind to certain targets in the body, such as molecules that cause the body to make an immune response (antigens). Olaparib is an inhibitor of PARP, an enzyme that helps repair deoxyribonucleic acid (DNA) when it becomes damaged. Blocking PARP may help keep tumor cells from repairing their damaged DNA, causing them to die. PARP inhibitors are a type of targeted therapy. Combination therapy with magrolimab and olaparib may be safe and effective in treating BRCA-mutated metastatic or recurrent breast or castrate-resistant prostate cancer.