Moreover, some cancer immunotherapy drugs including cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors (10), programmed cell death 1 (PD-1) inhibitors and programmed cell death 1 ligand 1 (PD-L1) inhibitors have been authorized by the United States Food and Drug Administration (FDA) for clinical use (13, 14). The gene discussed is PDCD1; the disease is cancer.