ESR1 and breast cancer: Compared with ER-positive breast cancer cells, the anti-proliferative effect of LRH-1 knockdown on the cell cycle is more pronounced in MCF-7 in the absence of E2 [15], in MCF7- derived anti-estrogen-resistant cell lines (MCF7/LCC2 and MCF7/LCC9) and in the ER-negative cell line BT-549 [1, 7].