CTLA4 and breast cancer: Among these therapy strategies, the United States Food and Drug Administration (FDA) has approved immune checkpoint inhibitors (ICIs) targeting PD-1 (programmed cell death receptor 1), PD-L1 (programmed cell death 1 ligand 1), and CTLA-4 (cytotoxic T-lymphocyte-associated antigen-4) for treatment of solid tumors such as BC (14, 15).