PDCD1 and melanoma: Subsequently, a variety of immune checkpoint inhibitors targeting PD-1/PD-L1 axis, such as nivolumab, atezolizumab, avelumab, and durvalumab, were approved for the treatment of non-small cell lung cancer, melanoma, renal cell carcinoma, bladder cancer, Hodgkin’s lymphoma, liver cancer, and gastric cancer (137).