PDCD1 and breast carcinoma: Strategies against breast cancer include: (1) targeting PD-L1 (programmed cell death receptor ligand 1), an immune checkpoint inhibitor; (2) inactivating the programmed cell death protein 1 (PD-1), which downregulates the immune system and promotes self-tolerance by CTL; and (3) inhibiting the cytotoxic T lymphocyte antigen-4 (CTLA-4) [Figure 3].