One of the major breakthroughs in cancer immunotherapy was the identification of immune checkpoint molecules, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), the programmed cell death-1 (PD-1), and its ligands programmed death-ligand 1 (PD-L1) and PD-L2 tumors. This evidence concerns the gene PDCD1 and cancer.