The ER-positive estrogen-dependent MCF-7 breast cancer cell line was compared with its estrogen-independent but tamoxifen and fulvestrant-sensitive cell line MCF-7/LCC1 [21] and the fully estrogen, tamoxifen and fulvestrant-resistant cell line MCF-7/LCC9 (LCC9; [22]). Here, ESR1 is linked to breast cancer.