Combination of Nivolumab Immunotherapy With Radiation Therapy and Androgen Deprivation Therapy

Inclusion Criteria: * Provision of signed and dated informed consent form. * Stated willingness to comply with all study procedures and availability for the duration of the study. * Male, aged ≥ 18 years * ECOG Performance Status: 0-1 * Diagnosed with Grade Group 5 prostate cancer (PCa): Gleason grade 9 (4+5 or 5+4) or 10 (5+5) with \>30% of cores involved; Any PSA or T-stage * Pathologically (histologically) proven diagnosis of PCa undergoing their first line of treatment * Biopsy specimen available * Patients with oligometastaic disease (defined as ≤3 sites of distant metastatic disease, and/or positive lymph nodes confined to the pelvis) being treated with curative intent are eligible for study participation * Eligible for definitive RT (HDR + EBRT) + short-term ADT * Undergoing radiation treatment at Moffitt Cancer Center * Participants being treated with nivolumab must have normal organ function as defined in protocol. * Males who are sexually active with women of childbearing potential must agree to follow instructions for method(s) of contraception for the duration of treatment with study drug plus 5 half-lives of the study drug (half-life up to 25 days) plus 90 days (duration of sperm turnover) for a total of 31 weeks post-treatment completion; Azoospermic males are exempt from contraceptive requirements; Male participants must be willing to refrain from sperm donation during the entire study and for 5 half-lives of study drug plus 90 days (duration of sperm turnover…