Metastasis is a major cause of morbidity and mortality in breast cancer with tumour cell invasion playing a crucial role in the metastatic process. The effects of a panel of phytoestrogens, including isoflavones and lignans on the invasion of a breast cancer cell-line (MDA-MB-231) through Matrigel were assessed. Genistein, glycitein, daidzein, equol, O-Desmethylangolensin (O-Dma) and coumestrol exerted a potent inhibitory effect on cell invasion (e.g. inhibition of 41.7 +/- 15% (P = 0.007); coumestrol (10 muM)). In contrast the lignans exerted minimal effects on invasion. Inhibition of invasion induced by the phytoestrogens occurred without affecting cell viability, highlighting the possible chemoprotective effects of these compounds. (C) 2003 Elsevier Ireland Ltd. All rights reserved.