CTLA4 and breast cancer: A poor prognosis can arise from immune evasion of breast cancer cells due to various immune factors that participate in immunosuppressive co-stimulation of receptors, including cytotoxic T lymphocyte-associated protein (CTLA)-4, programmed cell death-1 receptor (PD-1)40, and infiltration of suppressive immune cells (e.g., regulatory T cells (Tregs))41.