Currently, multiple antibodies against either PD-1 or PD-L1 are approved, mostly for the treatment of advanced metastatic cancers including metastatic melanoma, metastatic non-small-cell lung cancer (NSCLC), recurrent or metastatic head and neck cancer, refractory classical Hodgkins lymphoma, urothelial carcinoma, gastric cancer, and cancers with a biomarker referred to as high microsatellite instability (MSI-H). The gene discussed is PDCD1; the disease is cancer.