ESR1 and breast carcinoma: In this study, three well-established human mammary cell lines were chosen to represent a normal-like subtype (MCF10A; fibrocystic disease) and two cancer subtypes, luminal (MCF7; ESR1/PGR+) and basal-like metastatic (MDA-MB-231; ESR1/PGR- HER2-); together these provide a relatively comprehensive model to recapitulate the transitional differentiation observed in breast cancer subtypes, as it is difficult to mirror the heterogeneity associated with clinical samples with a single cell line [13, 14, 19].