Immune checkpoint inhibitors (ICIs), such as anti-CTLA-4 and anti-PD-1/PD-L1 monoclonal antibodies, which can unleash immunosuppression and reconstitute the antitumor immune response by reactivating dysfunctional or exhausted effector T cells, have achieved remarkable progress in treating patients bearing different types of cancer or in advanced stages [170–176]. This evidence concerns the gene PDCD1 and cancer.