(Integrative Medicine) - A series of animal studies conducted by researchers at the University of Illinois has found that the isoflavone genistein (a plant estrogen present in high concentrations in soy) may stimulate the growth of estrogen-dependent breast cancer tumors. Breast cancer cells that are estrogen-dependent need the hormone estrogen to grow. In the Journal of Nutrition, the researchers reported that dietary genistein stimulated the growth of human estrogen-dependent breast cancer cells implanted into experimental mice in a dose-dependent manner (as the dose of genistein increased, so did the growth of the tumors). The researches also reported in Carcinogenesis that dietary genistin (a substance related to genistein and the predominant form found in plants) stimulated estrogen-dependent breast cancer tumor growth in laboratory mice similar to that observed with genistein. Removal of these compounds from the diet caused the tumors to shrink in size. Findings published in Cancer Research indicated that soy protein containing varying concentrations of genistein also stimulated the growth of estrogen-dependent breast cancer tumors in a dose-dependent manner (similar to that observed with dietary genistein). "For the subgroup of postmenopausal women who have or are at high risk of developing breast cancer there is need for additional consideration into the possibility of enhancing estrogen-dependent tumor growth by consumption of isoflavone containing products," the researchers conclude.

References

Allred CD, Allred KF, Ju YH, Virant SM, Helferich WG. Soy diets containing varying amounts of genistein stimulate growth of estrogen-dependent (MCF-7) tumors in a dose-dependent manner. Cancer Res. 2001;61:5045-5050.

Allred CD, Ju YH, Allred KF, Chang J, Helferich WG. Dietary genistin stimulates growth of estrogen-dependent breast cancer tumors similar to that observed with genistein. Carcinogenesis. 2001;22(10):1667-1673.

Ju YH, Allred CD, Allred KF, et al. Physiological concentrations of dietary genistein dose-dependently stimulate growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in athymic nude mice. J Nutr. 2001;131:2957-2962.