ESR1 and breast cancer: Beyond drugs that directly target proteins such as ER, EGFR, HER2, MET, PI3K, AKT, mTOR, and those of the MAPK pathway [7], anti-apoptotic protein inhibitors (BH3 mimetics) are now being evaluated as new targeted therapies for breast cancer [35] as increased anti-apoptotic protein levels have been reported [33,35,40].