PDCD1 and cancer: Since the FDA approval of ipilimumab (cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) inhibitor) in 2011, six more ICIs have been approved for cancer therapy: the programmed cell death-1 (PD-1) inhibitors including nivolumab, pembrolizumab, cemiplimab, and the programmed cell death ligand-1 (PD-L1) inhibitors including atezolizumab, durvalumab, and avelumab.