Inhibition of tamoxifen's therapeutic benefit by tangeretin in mammary cancer

Tangeretin, a molecule present in citrus fruits and in certain 'natural' me nopausal medications, is an effective tumour growth and invasion inhibitor in vitro of human MCF 7/6 breast cancer cells. However, when added to the d rinking water of MCF 7/6 tumour-bearing mice it neutralises the beneficial tumour-suppressing effect of tamoxifen. Tangeretin reduces the number of na tural killer cells. This may explain why the beneficial suppressive effect of tangeretin on MCF 7/6 cell proliferation in vitro is completely countera cted in vivo. (C) 2000 Elsevier Science Ltd. All rights reserved.