The cancer preventive potential of tea polyphenol EGCG in HER2-positive breast cancer

Breast cancer is recognized as one of the leading causes of death among women in many countries and its incidence is closely linked to HER2 (human epidermal growth factor receptor 2) gene amplification. HER2, a second member of receptor tyrosine kinase of erbB family, is overexpressed in about 25% of human breast cancers with poor prognosis and chemoresistance, and considered as a target for breast cancer therapy. (-)-Epigallocatechin 3-gallate (EGCG), the most bioactive and abundant green tea catechin, has been thought as a chemopreventive agent by inhibition of growth and induction of apoptosis in various cancers including breast cancer. However, the molecular mechanisms responsible for cancer preventive effects of EGCG on breast cancer development are not fully elucidated. EGCG was found to suppress heregulin- β1-stimulated HER2/HER3 hetero-dimerization in breast cancer cells which initiates mitogenic signal transduction required for cancer progression. Also, the aggressive downstream phenotypes controlled by HER2 were inhibited by treatment of EGCG in breast cancer cells. These findings suggest that blockade of HER2/HER3 co-receptor formation by EGCG may be one of the possible cancer preventive mechanisms of EGCG in HER2-positive breast cancer.