ESR1 and breast carcinoma: Specifically, in breast cancer, preclinical in vitro and in vivo studies have been conducted on BT474 cells, in which the combination of OC with tamoxifen (an anti-estrogen) has been characterized by a reduction in the expression of estrogen receptor-alpha (ERα), an effect that could potentially enhance tamoxifen’s effectiveness in inhibiting the growth of breast cancer cells [48].