The Effect of Phytoestrogens on Normal Breast Tissue in Postmenopausal Women: Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Phytoestrogens are the active chemicals in soy products. Their chemical composition is similar to estrogen. Because the standard of care in the U.S. is to avoid estrogen replacement therapy in women with a history of breast cancer, phytoestrogens have been advocated for the relief of menopausal symptoms in women who cannot or do not want to use estrogen replacement. Phytoestrogens also may reduce the long-term risks of heart disease and osteoporosis. However, it is unclear what effect phytoestrogens have on breast cancer risk. Epidemiologic studies suggest that phytoestrogens are protective against breast cancer. However, few prospective clinical trials have been performed, and results in premenopausal women have shown mixed effects on breast cells. There is little data in postmenopausal women, and there have been no studies in postmenopausal breast cancer survivors.

The purpose of this research study is to investigate how taking phytoestrogens, in the form of isoflavone tablets, affects breast tissue changes. Isoflavones are the most active class of phytoestrogens, and are the most abundant in soy foods. Half of the study participants will receive active isoflavone tablets and half will receive inactive tablets (placebo). Study participants will be assigned by chance (like a flip of a coin) to one of two groups. The study will evaluate the effect of the phytoestrogens on breast tissue through scheduled biopsies of the uninvolved breast, before and after taking the soy tablets. The biopsy will be performed with a small needle and guided by ultrasound (sound waves). Data will also be gathered on common menopausal symptoms and dietary intake through the use of questionnaires.

Your participation will also provide us with much needed information about the use of phytoestrogens in postmenopausal women with a history of breast cancer.

This is a study for women who have experienced menopause, and who have breast cancer involving only one breast. Participants must be at least 30 years old, have completed their cancer therapy and are interested in study follow-up at Seattle Cancer Care Alliance. If you believe you are eligible for this study and are interested in participating, please contact the Phyto Hotline (206) 288-1444 or email us at phyto@u.washington.edu