PRIMARY OBJECTIVE:~I. To evaluate the disease control rate in metastatic castration-resistant prostate cancer (mCRPC) patients with non-measurable disease as assessed by Prostate Cancer Working Group 3 (PCWG3)-modified Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1~SECONDARY OBJECTIVES:~I. To evaluate the efficacy of the combination as measured by prostate-specific antigen (PSA) progression-free survival (PFS).~II. To evaluate the efficacy of the combination as measured by PSA 50% response rate.~III. To evaluate the efficacy of the combination as measured by radiographic progression-free survival (PFS).~IV. To evaluate the efficacy of the combination as measured by overall survival (OS).~V. To evaluate the safety of cabozantinib S-malate (cabozantinib) in combination with atezolizumab in patients with mCRPC with non-measurable disease.~EXPLORATORY OBJECTIVE:~I. To analyze tissue and tumor-based biomarkers to evaluate the mechanisms of treatment activity and resistance.~OUTLINE:~Patients receive cabozantinib orally (PO) once daily (QD) on days 1-21 and atezolizumab intravenously (IV) over 30-60 minutes on day 1. Cycles repeat every 21 days in the absence of disease progression or unacceptable toxicity.~After completion of study treatment, patients are followed up at 30 days and then every 3 months until disease progression or start of another therapy.
This phase II trial tests whether cabozantinib and atezolizumab work to shrink tumors in patients with castrate-resistant prostate cancer that had spread to other places in the body (metastatic). Cabozantinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Immunotherapy with monoclonal antibodies, such as atezolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving cabozantinib and atezolizumab may kill more tumor cells in patients with metastatic castrate-resistant prostate cancer.