#B178 The Effects of Soy on Mammographic Breast Density in a Randomized Trial.
Peter H. Gann, Catherine J. Moran, Kim E. Thedford, Ryan J. Deaton, R E. Hendrick, Irene B. Helenowski, Linda Van Horn,
Northwestern Univ. Medical School, Chicago, IL.
Soy-rich diets contain isoflavones and other compounds capable of interacting with endogenous estrogenic activity.
Previous research has suggested that soy intake can affect mammographic breast density, an independent marker of breast cancer risk.
We conducted a trial in which women at high risk for breast cancer were randomly assigned to isocaloric diets containing either 40 gms/day of soy or cows milk protein for 6 months.
Two-view mammograms were obtained before and after intervention, and these were blindly analyzed for total dense area and percent density using digital image analysis with operator-set density thresholds.
36 women had both pre- and post-treatment mammograms available for analysis. 32 women provided density measurements from both breasts, and 4 from a single breast due to a prior mastectomy. 75% of subjects were pre- or perimenopausal, 17% had a prior history of breast cancer or DCIS in the opposite breast, 67% had a first-degree relative with breast cancer, and their mean age was 46.6 years.
In the soy group, serum genistein and daidzein increased on average by 498 ng/ml (139-fold) and 151 ng/ml (41-fold) while on-study, compared to mean increases of 2.3 ng/ml for serum levels of both isoflavones among milk controls.
Mean breast density percent at baseline was 41.8% and 39.4% in the milk (n=19) and soy (n=17) groups, respectively. The mean change in density % was +2.8% (95% CI: - 0.6, 6.2) and +1.3% (95% CI: - 0.7, 3.3) in the milk and soy groups.
The results were unchanged following adjustment for baseline age, smoking, menopausal status, parity, physical activity, and body mass index.
Furthermore, the soy vs milk effects on breast density were similar when subjects were stratified on these variables.
There were no evident soy effects on breast density when analysis was restricted to women who reported consuming at least 80% of their prescribed dose (72% of participants reported this level of compliance).
In conclusion, 6 months of soy supplementation had no effect on mammographic breast density in this trial involving middle-aged women at high risk for breast cancer.
Effects due to exposure that begins earlier in lifeor that persists for a longer period cannot be ruled out.
Frontiers in Cancer Prevention Research, 2003
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