Knock down of EGFR reverses tamoxifen resistance of MCF7-EGFR cells and is ERα independent. EGFR (A) and ERα (C) knockdown in MCF7 parental and MCF7-EGFR cells was established using siRNA. Knock down efficiency and the effect of EGFR knock down on phosphorylation status of MAPK1/3 and Akt after 30 min EGF (100 ng/mL) exposure was analysed on western blot. GFP siRNA was used as control. (A, C) After 48 hours starvation knock down cells were exposed to 0.1 nM E2 plus 100 nM TAM and 100 ng/mL EGF. Proliferation was measured after 5 days using sulforhodamin B absorbance at 540 nm (B, D). Graphs represent the average ± SEM of three (A, B) or four (C, D) individual experiments, * indicates significantly different at p < 0.05; # indicates significantly different at p < 0.01.