Subjects enrolled in cohort 1 of Phase 1 of the protocol will receive durvalumab monotherapy with no randomization. For all other study cohorts in both Phase 1 and Phase 2 of the protocol, subjects registered at self-identified EBRT+ study sites will be randomized 1:1 between all actively accruing study arms while subjects registered at self-identified EBRT- study sites will be randomized 1:1 between all actively accruing study arms except the durvalumab + EBRT arm.