MCF7-EGFR tamoxifen resistance involves PI3K/Akt pathway. Parental MCF7 and MCF7-EGFR cells were starved for 48 hrs before pre-treatment with either the MEK inhibitor U0126 (10 μM) or the PI3K inhibitor BEZ235 (1 μM) for 30 min. The effect of inhibition on EGF-induced activation of MAPK1/3 and Akt was analyzed on western blot (A). Following U0126 and BEZ235 pre-treatment cells were exposed to 0.1 nM E2, 100 nM TAM and 100 ng/mL EGF. Proliferation was measured after 5 days using sulforhodamin B absorbance at 540 nm (B, C). Graphs represent the average ± SEM of three independent experiments, * indicates significant difference of p < 0.05, # indicates significant difference of p < 0.01.