Soy Isoflavones and Breast Cancer Risk Reduction

Soy consumption has been associated with reduced risk for developing breast cancer. Soy contains isoflavones which are weak estrogens. The roles of soy isoflavones in reducing breast cancer risk are currently unclear. Breast density has been considered as a breast cancer risk marker. We hypothesize that because isoflavones have estrogen-like activities, breast density and possibly bone density will be lower in women on soy-isoflavones.

This is a randomized, double-blind study, with two arms and 100 women in each arm. Premenopausal women will be recruited and randomly allocated to take one of the two different dietary supplements in pills daily for 2 years. The two supplements are soy isoflavones (treatment) and placebo (carbohydrates). Both treatment and placebo pills will contain multi-vitamins and minerals. Multiple blood, urine, and breast fluid samples will be obtained before and during the dietary supplement periods and analyzed for biomarkers of breast cancer risk. At baseline and after the intervention period, breast density and bone density will be assessed by radiologic techniques. The efficacy of the dietary intervention will be determined by comparing mean changes of serum markers for breast cancer risk,dense breast tissue, and bone mineral density over the two year dietary intervention period in the two supplement groups with adjustment for baseline values and individual patient characteristics of interest. We predict that 2 years of soy isoflavone supplement will reduce breast density, which may be explained by individual changes in serum markers of breast cancer risk.

• Dietary Supplement: isoflavones
  soy isoflavones: Each tablet contains 246 mg Novasoy, 676 mg calcium, 15 mg riboflavin, and other innert materials to a total weight of 1000 mg. Subject takes two isoflavone tablets plus 1 multi-vitamin per day for five days per week for upto 2 years.
  Other Name: Isoflavone pill
• Dietary Supplement: carbohydrate
  carbohydrate: 246 mg maltodextrin, 676 mg calcium, 15 mg riboflavin and other innert ingredients to a total weight of 1000 mg per tablet. subject takes two tablets plus one multivitamin per day for five days per week for upto 2 years.
  Other Name: Sugar pill

• Experimental: 1
  soy isoflavones
  Intervention: Dietary Supplement: isoflavones
• Placebo Comparator: 2
  carbohydrates (maltodextrin)
  Intervention: Dietary Supplement: carbohydrate

Inclusion Criteria:

• healthy premenopausal women
• 30 to 42 years old
• normal mammograms
• regular menstrual cycles

Exclusion Criteria:

• abnormal mammograms
• first degree relatives with breast cancer
• pregnant or lactating
• peri- or post-menopause
• breast augmentation, reduction or lifting
• on oral contraceptive medications or exogenous hormones
• medically prescribed diets
• allergic reaction to soy products

• National Cancer Institute (NCI)
• National Center for Research Resources (NCRR)