Agents that block PD‐1/PD‐L1 have exhibited dramatic antitumor efficacy in clinical trials for patients with a variety of cancer types.3, 4, 5 PD‐1 and its ligand, PD‐L1, play a major role in the cancer microenvironment, and expression of these molecules is related to not only prognosis but is also a useful predictive factor for the therapeutic effect of anti‐PD‐1 or anti‐PD‐L1 immunotherapies in various malignancies.6 This evidence concerns the gene PDCD1 and cancer.