ESR1 and breast adenocarcinoma: A G2/M arrest followed by the induction of apoptosis was however observed in cell lines including tumorigenic estrogen receptor positive breast carcinoma cell line (MCF-7), drug resistant human adenocarcinoma cell line (MCF-7 DOX40), mitoxantrone resistant breast adenocarcinoma cell line (MCF-7 MR) and highly tumorigenic estrogen receptor negative breast carcinoma cell line MDA-MB-231 [8,17].