Durvalumab and Tremelimumab in Treating Chemotherapy Naive Patients With Metastatic Castration-Resistant Prostate Cancer

PRIMARY OBJECTIVE: I. To evaluate the safety and tolerability of durvalumab plus tremelimumab in patients with metastatic castration-resistant prostate cancer. SECONDARY OBJECTIVES: I. To assess the efficacy of durvalumab plus tremelimumab in patients with metastatic castration-resistant prostate cancer. II. To explore immunological changes in peripheral blood and tissue (e.g. peripheral blood cluster of differentiation \[CD\] 4+ \[Inducible COStimulator (ICOS)\]+ T cells, CD3 expression in tissue) in response to durvalumab plus tremelimumab in patients with metastatic castration-resistant prostate cancer. OUTLINE: Patients receive tremelimumab intravenously (IV) over 60 minutes and durvalumab IV over 60 minutes on day 1. Treatment repeats every 28 days for up to 4 cycles for tremelimumab and up to 13 cycles for durvalumab in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30, 60, and 90 days, and then every 3 months thereafter.