Basic and Epidemiological study for the carcinogenic role of obesity and nutritional factors in breast and colon cancers

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Incidence of breast and colon cancer is increasing recently among Japanese women. As these cancers are considered to be obesity- and diet-linked diseases, we have investigated the association of breast carcinogenesis with visceral fat obesity and dietary factors through in vivo, in vitro, and epidemiological approaches. Model rats for visceral obesity did not produce any tumor 40 weeks after oral administration of ethylmethane sulphonate (EMS), while a control rats produced tumors in 2 rats out of 16 rats. Genistein (GEN), a phytochemical with weak estrogenic activity, did not suppress the incidence of EMS-induced hormone-dependent tumor in WKA rats fed on diets with low to high concentrations of GEN. A case-control study suggests that intakes of oil and plant lipids were associated with elevated risk for breast cancer, but not with Soybean intake in postmenopausal Japanese women. These results suggest that Soybean isoflavone may not reduce the risk of breast cancer for postmenopausal women.