PDCD1 and neoplasm: Immune checkpoint inhibitors, including Programmed Cell Death Protein 1 (PD-1)/Programmed Death-Ligand 1 (PD-L1) and Cytotoxic T Lymphocyte-Associated Antigen 4 (CTLA-4) inhibitors, invigorate the immune response against tumors by disrupting the suppressive signals exchanged between tumor and immune cells.