It is estimated that the proportion of patients with cancer eligible to receive one or more of the programmed cell death-1 (PD-1), programmed cell death-ligand 1 (PD-L1), or cytotoxic T lymphocyte associated antigen-4 (CTLA-4) ICIs has increased from 1.5% in 2011 to 43.6% in 2018 (1). This evidence concerns the gene PDCD1 and cancer.