PDCD1 and neoplasm: Immunotherapies, represented by ICIs such as various antibodies against cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), programmed cell death 1 (PD-1), and programmed cell death ligand 1 (PD-L1), are designed to stimulate the patient’s immune system to trigger an effective anti-tumor immune response (Rosenberg, 2014).