Soy and Breast Cancer Prevention
(PI: L. Lu)Populations consuming high levels of soy, as in many Asian countries, have lower levels of ovarian hormones, lower rates of breast cancer, and reduced mammographic density than populations consuming typical Western diets. These observations may in part be explained by our clinical studies that found ovarian hormone levels of premenopausal women to be lowest while they were consuming a diet that provided 15% energy from soymilk containing weakly estrogenic isoflavones. Further questions are whether isoflavones and/or soy proteins are the critical components influencing breast cancer risk, which are being tested by two randomized, double-blind, placebo controlled clinical trials (www.clinicaltrials.gov and the identifiers are NCT00204477 and NCT00204490).Women with dense breasts have a 4-6 fold excess risk of developing breast cancer. Moreover, greater breast density makes it more difficult to detect early breast cancer by mammography. In one trial (funded by NIH), the effect on breast density of 2-year supplementation with pills of soy isoflavones (treatment) is being compared with pills without isoflavones (placebo). In the second trial (funded by Army’s Breast Cancer Research Program), the effect on breast density of 2-year supplementation with soy protein without isoflavones (treatment) is being compared with cow’s milk proteins without other female hormones (placebo). Reducing breast density by soy isoflavones and/or soy proteins can be expected to reduce the volume of target tissue at risk for breast cancer development and will improve the sensitivity of mammography for screening. The study may lead to a novel, non-invasive and economical approach to breast cancer prevention.