ESR1 and breast cancer: To address whether stromal cells can alter CLA-induced apoptosis in ERα(+) and ERα(-) cancer epithelial cells, breast cancer epithelial cell lines, MCF-7, MDA-MB-231, or MDA-MB-231-ERα, were co-cultured with primary human breast stromal cells isolated from normal (NSC) or cancerous (CASC) tissues.