CD8A and neoplasm: In breast cancer, PARPi have been shown to increase tumor cell expression of PD-L1, thereby suppressing the antitumor T cell response, but also to have a synergistic effect when given with PD-1 inhibition.101 This effect may be due at least in part to inhibition of PARP-mediated CD8+ T cell apoptosis driven by reactive oxygen species produced by tumor cells.102 The Topacio/Keynote-162 trial evaluated niraparib and pembrolizumab in a phase II single arm trial with an ORR of 28% and disease control rate of 50%, with the best responses being demonstrated in patients with a tumor BRCA mutation.15