The first successful pathway involved the programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) pathways, which are key mediators through which cancer cells evade antitumor T-cell-mediated cytotoxicity (13). This evidence concerns the gene PDCD1 and cancer.