PDCD1 and cancer: The FDA (Food and Drug Administration) has approved several groups of ICIs to treat a variety of cancers: ipilimumab (CTLA-4 inhibitor); nivolumab, pembrolizumab, and cemiplimab (PD-1 inhibitors); atezolizumab, durvalumab, and avelumab (PD-L1 inhibitors) [54].