The PD-1/PD-L1 antibody was recently approved by the FDA for metastatic melanoma, non-small cell lung cancer (NSCLC), head and neck, kidney and urothelial carcinomas, Hodgkin lymphoma, and microsatellite instability/mismatch repair (MMR) deficient cancers [43]. Here, PDCD1 is linked to metastatic melanoma.