Immune checkpoint inhibitors (ICIs), by targeting cytotoxic-T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death 1 (PD-1), or PD-ligand 1 (PD-L1), have yielded durable anti-tumor responses and long-term remissions in non–small cell lung cancer (NSCLC) and other cancer types. This evidence concerns the gene PDCD1 and cancer.