Differential response to phytoestrogens in endocrine sensitive and resistant breast cancer cells in vitro

Women approaching menopause increasingly investigate alternatives to hormone replacement therapy. Plant phytoestrogens are being promoted as “natural” alternatives but there is a lack of substantive data to advocate their safe use in breast cancer patients receiving tamoxifen (TAM), or in those who have relapsed. The aim of our study was to investigate the proliferative effects and mode of action of the phytoestrogens genistein, daidzein and coumestrol on TAM‐sensitive (‐s) and resistant (‐r) breast cancer cells under in vitro conditions designed to mimic the hormonal environment of the pre‐ and post‐menopausal breast. At physiological concentrations (