ESR1 and breast cancer: By taking into account that ER(α) overexpression is related to increased proliferation and metastasis in BC, while ER(β) function remains elusive, it may have a bi-faceted role in BC, based on our results showing that H19 and telomerase levels increase after ER(α) or ER(β) overexpression and considering that the latter can be involved in glycolysis modulation, ATRA treated or untreated MDA-MB-231 cells, triple-negative cells, were transfected with ER(α) or ER(β) expression plasmids for 48 h.