Overview of research on the relationship between soya intake and breast cancer and potential mechanisms by which soya affects breast cancer risk

摘要

Soyafoods have attracted the attention of the research community for their purported health benefits. One reason for the interest in soya is because the soyabean is essentially a unique naturally dietary source of isoflavones. Isoflavones are often referred to as phytoestrogens although they differ from estrogen and are frequently classified as selective estrogen receptor modulators (SERMs), such as the breast cancer drug tamoxifen and the osteoporosis drug raloxifene. Furthermore, isoflavones have important non-hormonal properties. The relationship between soya intake and breast cancer risk has been actively investigated for approximately 15 years. Certainly, the low breast cancer rates in Asia helped fuel initial enthusiasm in soya. Additionally,the knowledge that estrogen-like compounds such as isoflavones have the potential to exert antiestrogenic effects under some experimental conditions provided a possible mechanism by which soya could reduce breast cancer risk. However, beginning in the late 1980s, focus began to shift to the effects of genistein, the main isoflavone in soyabeans, on signal transduction. In vitro, genistein inhibits the growth of both estrogen-dependent and independent breast cancer cells although high concentrations arerequired. Furthermore, at low concentrations, genistein stimulates the growth of estrogen-receptor positive breast cancer cells. Animal studies generally indicate that isoflavone-rich soya protein and isolated isoflavones inhibit chemically induced mammary cancer and inhibit the growth of tumors in mice implanted with mammary cancer cells. Although again, in some experimental models growth is enhanced. In contrast to the animal studies, there is relatively little epidemiologic support for the hypothesisthat adult soya consumption is protective against breast cancer. Results from clinical studies involving markers of breast cancer risk such as serum estrogen levels and estrogen metabolism, cell proliferation, and breast tissue density are, mixed.