Inhibition of Src kinase prevents tamoxifen-induced cellular invasion in E-cadherin deficient MCF-7 cells. (a) MCF-7 cells were treated with CDH1 siRNA and tamoxifen in the presence or absence of the Src kinase inhibitor, SU6656 (2.5 μM). SU6656 inhibited Src kinase activity in each of the samples examined. (b) MCF-7 cell invasion was determined in E-cadherin deficient MCF-7 cells in the presence of tamoxifen alone, or tamoxifen plus the epidermal growth factor receptor (EGFR) inhibitor, gefitinib ('TKI'), the Src inhibitor, SU6656 ('SU') or the human epidermal growth factor receptor 2 (HER2) inhibitor, herceptin ('Her'). Inhibition of Src activity prevented the tamoxifen-induced invasion in E-cadherin-deficient cells. *p < 0.05 versus cells treated with siRNA and tamoxifen. (c) Cell growth in the presence of the same inhibitors was determined by counting the numbers of cells present in the wells of a 24-well plate after 72 hours treatment as shown. No treatment significantly affected cellular growth over this time period.