The currently approved (2) systemically administered checkpoint inhibitors have improved metastatic disease survival by targeting the T cell co-inhibitory pathways of CTLA-4 (cytotoxic T-lymphocyte associated protein 4; ipilimumab (3, 4) tremelimumab (5, 6)), PD-1/PD-L1 (programmed cell death protein 1/programmed death-ligand 1; nivolumab, pembrolizumab, cemiplimab, atezolizumab, avelumab, durvalumab (4), dostarlimab (7)) and LAG-3 (lymphocyte-activation gene 3; relatlimab (8)). This evidence concerns the gene PDCD1 and metastatic neoplasm.