PDCD1 and cancer: The most interesting results in various cancers come from studies of three antibodies: anti-programmed cell death protein 1 (anti-PD-1), anti-programmed cell death protein ligand 1 (anti-PD-L1), and anti-cytotoxic T-lymphocyte antigen 4 (anti-CTLA-4) [183,357,358,359,360].