MCF−7/SC cells displayed resistance to tamoxifen. Viability of MCF−7 and MCF−7/SC cells was determined after tamoxifen treatment for 24 h (A) and 48 h (B). The effect of tamoxifen on (C,D) colony formation, (E,F) migration, and (G,H) invasive capacity was compared between MCF−7 and MCF−7/SC cells. (I,J) The apoptotic population detected after tamoxifen treatment. (K,L) Western blot analysis for apoptosis markers after tamoxifen exposure. β−actin was used as a loading control. The asterisk (*) indicates p < 0.05 vs. the control. Data were representative of three biologically independent experiments and values were shown in mean ± SD.