PDCD1 and cancer: FDA-approved drugs, such as cemiplimab, ipilimumab, nivolumab and pembrolizumab, targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) checkpoints, have had a profound effect on patients with various types of cancer, including melanoma, non-small cell lung cancer, renal cell cancer and classical Hodgkin lymphoma (3,4).