Effect of tamoxifen on breast cancer cell lines growth. (A) Inhibition of breast cancer cell growth by tamoxifen after 6 days. Data are mean and s.e. of three independent experiments. Left – graphs showing MCF7, MMU2 and LCC9 cell growth inhibition. Right – graphs showing MCF7, T47D, MDA-MB-231 and HCC1937 cell growth inhibition. (B) Tamoxifen concentrations required to inhibit breast cancer cell growth by 50% of that of vehicle-treated control over a 6-day period. Bars show mean and s.e. of concentrations from three independent experiments.