PDCD1 and neoplasm: In line with the usage of PARPi in DDR-deficient tumors (266), PARPi combined with immune checkpoint blockade, including PD-1/PD-L1 and CTLA-4, exerts remarkable efficacy in tumors with BRCA1/2 or ERCC1 mutations via STING-dependent immune responses and infiltration of cytotoxic T cells into tumor (50, 51, 54, 270).