Breast cancer is the most common cancer among women worldwide and constitutes an international major health problem, mainly because of uncontrolled proliferation and aggressive metastatic behaviour. In the metastatic cascade, migration is one of the crucial steps responsible for death in breast cancer. Numerous studies have reported the involvement of potassium (K+) channels in the regulation of cell proliferation and apoptosis. Previous works from our laboratory have shown that hEag1 K+ channel is crucial for breast cancer cell proliferation and cell cycle progression in non-metastatic breast epithelial cancer cells MCF-7 (1). However, the role of these K+ channels in tumour cell dissemination and metastasis has been not yet investigated. In this study, we used the metastatic breast cancer cell line MDA-MB-231 to investigate the role of hEag1 K+ channels in migration. hEag1 K+ channel is not expressed, at the protein level, in normal breast epithelial cells such as hTERT (human mammary epithelium immortalized with telomerase) or MCF-10A. In contrast, hEag1 K+ channel is expressed at a high level in both the non invasive (MCF-7) and invasive breast cancer cells (MDA-MB-231). Moreover, in MDA-MB-231, inhibition of hEag1 by astemizole (the more selective hEag1 channel inhibitor), or by siRNA, decreased cell migration in transwell assay by 26.3 ± 0.9% and 87.3 ± 1.8% respectively (n=3, p<0.01; n=3, p<0.01; Student test). Similar results were obtained in HEK-293 cells stably transfected with hEag1 (65.9 ± 9.3% inhibition with astemizole, n=3, p<0.01, Student test). Migration of tumour cells is associated with the expression/activation of several proteins in the focal adhesion complex, including focal adhesion kinase (FAK) and several integrins. In MDA-MB-231, we found that the inhibition of migration induced by sihEag1 was correlated to a down-regulation of integrin beta-1, integrin beta-3 and FAK expression. Furthermore, knockdown of hEag1 by siRNA inhibited also the kinetics of the FAK phosphorylation. Taken together, our results provide evidence of the involvement of hEag1 K+ channel in breast cancer migration through a mechanism dependent of beta-1, beta-3 integrins and FAK.