PDCD1 and cancer: Although new therapies that target proteins such as antibodies against programmed cell death 1 (PD-1), programmed death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have ushered in a new era in cancer pharmacotherapy and drug development, some oncogene-encoded protein targets are intractable or insufficient for achieving remission.