ESR1 and breast carcinoma: Indeed, tamoxifen regulates transcription of subsets of estrogen target genes in endometrial carcinoma cell lines (Ishikawa, ECC-1) and also in ER+ breast cancer cell lines (MCF-7, ZR-75-1), in addition to altering expression of sets of genes apparently not regulated by estradiol via mechanisms that remain to be clarified (Shang & Brown 2002, Frasor et al. 2004, Scafoglio et al. 2006, Chang et al. 2010, Wardell et al. 2012, Tamm-Rosenstein et al. 2013).