Specifically, beyond PD-1–PD-L1 and CTLA-4, other checkpoint inhibitors are being developed, as well as new IO approaches, such as cancer vaccines, adoptive cell therapy with chimeric antibody receptor-expressing T cells (CAR-T), small molecule modulators of immune response (e.g., toll-like receptor (TLR) agonists), and nucleic acid-based therapies. This evidence concerns the gene PDCD1 and cancer.