ESR1 and breast cancer: To determine the effect of TAM, CXB, and both on the cell viability of breast cancer cells in vitro, ER-α-positive MCF7 and T-47D cells and ER-α-negative MDA-MB-231 and MDA-MB-468 cells were treated with increasing concentrations of CXB (0–250 μM) or TAM (0–40 μM).