PDCD1 and neoplasm: Immune checkpoint inhibitors are able to block immunological checkpoint molecules, such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and programmed death ligand 1 (PD-L1), and the goal of their inhibition is to boost the T lymphocytes’ immunological response against tumor cells.