PDCD1 and cancer: To date, several therapeutic monoclonal antibodies that target either PD-1 (nivolumab, pembrolizumab) or PD-L1 (avelumab, atezolizumab, durvalumab) have been FDA approved for treating various cancers such as melanoma, kidney, bladder, gastric, lung and head and neck cancers [5,6,7,8,9,10,11,12,13,14,15].