Checkpoint inhibitors, particularly PD1 pathway blockade, have been approved by the FDA for a number of indications, including advanced melanoma, head and neck cancer, renal cell carcinoma, non-small cell lung cancer (NSCLC), urothelial carcinoma, and metastatic Merkel-cell carcinoma, due to enhanced survival benefits compared to traditional chemotherapy. Here, PDCD1 is linked to melanoma.