Cancer immunotherapy using immune checkpoint blockade, particularly antibodies against programmed cell death receptor 1 (PD-1) or its ligand (PD-L1), has made a revolution in cancer treatments as this treatment has durable response even to terminal stage cancers and lesser side-effects compared to the conventional cancer treatments (Brahmer et al., 2010; Couzin-Frankel, 2013; Hodi et al., 2010; Mahoney et al., 2015; Topalian et al., 2015). This evidence concerns the gene PDCD1 and cancer.