PDCD1 and cancer: Immune checkpoint inhibitors (ICIs) have become a powerful clinical strategy for treating cancer, including an antibody targeting cytotoxic T lymphocyte-associated antigen-4 (CTLA-4, e.g., ipilimumab), antibodies directed against programmed cell death protein-1 (PD-1, e.g., nivolumab, pembrolizumab, and cemiplimab), and anti-PD-1 ligand (PD-L1, e.g., atezolizumab, durvalumab, and avelumab) [1].