In 2012 breast cancer is still the most common cancer among women worldwide, and its incidence and mortality are still increasing. Therefore, health care procedures for breast cancer patients and survivors are still very important. Many breast cancer patients increase their soy consumption because they believe in the anticancer effect of isoflavones. In Asian countries, where more soy is consumed than in Western countries, breast cancer incidence is relatively lower. On the other hand, it still remains controversial whether isoflavones are safe for breast cancer patients or women with high risk for developing breast cancer. It is still unknown whether isoflavones present a risk factor for breast cancer. Youngjoo Kwon of the Department of Food Science and Engineering (Ewha Womans University at Seoul) investigated the findings form different preclinical studies.
Youngjoo Kwon found that high concentrations of isoflavones inhibit the proliferation of breast cancer cells, regardless of their estrogen receptor status. On the other hand, the isoflavone genistein stimulates tumor growth at low concentrations and mitigated tamoxifen efficacy in estrogen receptor-positive breast cancer. Not only genistein levels but also the relative levels of genistein and estrogen are important to determine the genistein effect on the estrogen receptor-positive tumor growth. Studies conducted on ovariectomized mice and subcutaneous xenograft models, which show extremely low estrogen levels compared to human breast tumors, cannot be translated to humans. The author believes that it is an oversimplification that isoflavones stimulate hormone-dependent tumor growth due to their potential estrogenic effect. Isoflavones may exert nonestrogenic anticancer effects.
He concluded that futures studies should take into account the concentrations of isoflavones and estrogen in human breast tumors. There is still a lot of work to identify the molecular mechanisms by which isoflavones either inhibit or promote the growth of breast cancer cells.
Youngjoo Kwon. Effect of soy isoflavones on the growth of human breast tumors: findings from preclinical studies. Food Sci Nutr. 2014 Nov;2(6):613-622.