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Limer JL, Speirs V.
Molecular Medicine Unit, University of Leeds, St James's University Hospital,
Leeds, UK.
Phytoestrogens are polyphenol compounds of plant origin that exhibit a
structural similarity to the mammalian steroid hormone 17beta-oestradiol. In
Asian nations the staple consumption of phyto-oestrogen-rich foodstuffs
correlates with a reduced incidence of breast cancer. Human dietary intervention
trials have noted a direct relationship between phyto-oestrogen ingestion and a
favourable hormonal profile associated with decreased breast cancer risk.
However, these studies failed to ascertain the precise effect of dietary
phyto-oestrogens on the proliferation of mammary tissue. Epidemiological and
rodent studies crucially suggest that breast cancer chemoprevention by dietary
phyto-oestrogen compounds is dependent on ingestion before puberty, when the
mammary gland is relatively immature. Phyto-oestrogen supplements are
commercially marketed for use by postmenopausal women as natural and safe
alternatives to hormone replacement therapy. Of current concern is the effect of
phyto-oestrogen compounds on the growth of pre-existing breast tumours. Data are
contradictory, with cell culture studies reporting both the oestrogenic
stimulation of oestrogen receptor-positive breast cancer cell lines and the
antagonism of tamoxifen activity at physiological phyto-oestrogen
concentrations. Conversely, phyto-oestrogen ingestion by rodents is associated
with the development of less aggressive breast tumours with reduced metastatic
potential. Despite the present ambiguity, current data do suggest a potential
benefit from use of phyto-oestrogens in breast cancer chemoprevention and
therapy. These aspects are discussed.