ESR1 and breast cancer: The necessity of ERα for estrogen-induced growth inhibition and apoptosis was confirmed by Obiorah et al. (2014) who showed that the phytoestrogen genistein induced endoplasmic reticulum stress, an inflammatory response leading to intrinsic and extrinsic apoptosis in a long-term estrogen-deprived BC cell line (MCF-7:5C) through an ERα-mediated mechanism.