ESR1 and breast carcinoma: When two estrogen receptor- and PR-positive human breast cancer cell lines (BT-474 and T47-D) were exposed for 24 or 48 h to varying concentrations of LU (0–100 μM) used in previous studies (Seelinger et al. 2008), LU markedly reduced cell viability in both a time- and dose-dependent manner (Fig. 1a, b).