Immune checkpoint inhibitors (including anti-PD-1 antibodies, anti-PD-L1 antibodies, anti-CTLA-4 antibodies, and their combinations) have revolutionized cancer treatment, showing higher efficacy than standard therapies in several cancers, including melanoma [19,20,21,22,23,24,25], non-small cell lung cancer (NSCLC) [26,27,28,29,30,31], head and neck squamous-cell carcinoma [32], and renal cell carcinoma (RCC) [33]. This evidence concerns the gene PDCD1 and cancer.