Pembro With Radiation With or Without Olaparib

Immunotherapy and PARP-inhibitor are known to have radio-sensitizing effects when combined with radiation therapy. In addition, the combination with PARP-inhibitor and radiation can increase neoantigen expression, cytotoxic lymphocyte infiltration within the tumor microenvironment and increased immune stimulating cytokine concentration. Thus, there is a potential synergy of combining immunotherapy and PARP-inhibitor. This is a phase 2 randomized 1:1 study. Subjects will be randomized to one arm (pembro + PARPi + standard of care therapy which is definitive radiation therapy combined with hormonal therapy) vs. another arm (pembro + standard of care therapy). All subjects will receive adjuvant immunotherapy for one year once they are done with definitive radiation treatment. Due to slow accrual and feasibility concerns, the protocol was modified to single arm phase II study. All patients will receive definitive radiation therapy combined with ADT per institutional standards. In addition to concurrent ADT and radiation therapy, patients on this trial will also receive as follow: Pembrolizumab (17 cycles) combined with olaparib (the first three cycles). The remaining patients will be enrolled to Arm 1 only (i.e., Arm 2 usual care is closed to accrual upon Amendment 5 protocol).