At the latest since the Nobel Prize was presented to Tasuku Honjo and James P. Allison in 2018, immune checkpoint inhibitors, including programmed cell death protein-1 (PD-1) or cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4), have been ubiquitously present in the treatment of cancer. The gene discussed is PDCD1; the disease is cancer.