PDCD1 and neoplasm: Immune checkpoint inhibitors (ICIs) including antibodies against cytotoxic T-lymphocyte antigen 4 (CTLA-4) or programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) act to reverse the immunosuppression imparted by tumor cells, either by blocking CTLA-4 pathway or interrupting the interaction between PD-1 and PD-L1 (8, 9).