Immune checkpoint inhibitors (ICIs), including anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) antibodies and agents directed against the programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1), have demonstrated to be effective in the treatment of numerous cancers, including advanced melanoma, non-small and small lung cancer, renal carcinoma and hepatocellular carcinoma among many others [1]. The gene discussed is PDCD1; the disease is cancer.