PDCD1 and cancer: For other common cancers, including breast cancer, immunotherapy, in particular with the most known FDA approved immune checkpoint blockers, such as PD-1 (programmed cell death protein 1), PD-L1 (programmed death-ligand 1), and CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), have been shown a low success rate (9, 10), with only Atezolizumab (anti-PD-L1) being approved for the treatment of metastatic triple negative breast cancer (TNBC).