PDCD1 and neoplasm: Over the past decade, tumor immunotherapy has shown its unique advantages and good clinical efficacy in the treatment of malignant tumors, and numerous immune checkpoint inhibitors that target cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1)/programmed death-ligand 1 (PD-L1) including ipilimumab [1], nivolumab, and pembrolizumab [2] have been approved by the Food and Drug Administration (FDA).