ESR1 and breast cancer: Furthermore, a study revealed that the presence of ERα is necessary for growth inhibition and apoptosis induced by α-mangostin in human breast cancer cells, as evidenced by that MDA-MB-231 cells (ER-α negative) is less sensitive to α-mangostin than MCF-7 cells (ERα positive), and that knockdown of ERα reduced the cell growth inhibition and caspase-7 activation induced by α-mangostin [109].