Up until now, FDA approved PD-1 and PD-L1 checkpoint inhibitors for melanoma, renal cell carcinoma, head and neck cancer, urothelial carcinoma, CRC, hepatocellular carcinoma, small and non-small cell lung cancer, esophageal squamous cell carcinoma, cervical cancer, Merkel cell carcinoma, bladder cancer, certain types of endometrial carcinoma, and breast cancer. Here, PDCD1 is linked to melanoma.