Hormone Therapy and Ipilimumab in Treating Patients With Advanced Prostate Cancer

RATIONALE: Androgens can cause the growth of prostate cancer cells. Antihormone therapy, such as leuprolide acetate, goserelin, flutamide, or bicalutamide may lessen the amount of androgens made by the body. Monoclonal antibodies, such as ipilimumab, can block cancer growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry cancer-killing substances to them. Giving antihormone therapy together with ipilimumab may kill more tumor cells. PURPOSE: This randomized phase II trial is study how well giving hormone therapy and ipilimumab together works in treating patients with advanced prostate cancer.