Key discoveries, such as the immune checkpoints and their role in cancer progression, have ultimately led to novel interventions with durable responses and improved clinical outcomes, such as the inhibitors of cytotoxic T-lymphocyte associated protein-4 (CTLA-4), the programmed cell death-1 (PD-1) and its ligand (PD-L1), and lymphocyte activation gene-3 (LAG-3) [2]. This evidence concerns the gene PDCD1 and cancer.