PDCD1 and neoplasm: The great clinical achievements of antagonizing monoclonal antibodies against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1), called checkpoint inhibitors (CPIs), have clearly proven that the immune system is capable of eradicating tumor cells, validating the concept of harnessing the patient’s own immune system to control cancer1.