783

Women with very dense breasts have a 4 to 6-fold greater risk for breast cancer compared to women with little or no dense breast tissue. This study investigated factors influencing breast density in healthy, 30-40 year old premenopausal women who were not taking contraceptive medications and not lactating. Subjects were recruited by postal and web mails from a 50-mile radius from Galveston. Mammograms were obtained during the luteal phase of a menstrual cycle using a FDA approved full field digital mammography (FFDM) unit. Mammograms from the cranial-caudal view of the left breast were analyzed for breast density by a modified computer-assisted image analysis method that is based on histogram segmentation methodology. Fasting blood was also obtained during the luteal phase of the menstrual cycle and the plasma analyzed for progesterone. Nutrient intakes were estimated by food frequency questionnaire. Pearson correlation coefficients showed that left breast density correlated significantly (P<0.05) with %-body fat (r=-0.42), body mass index (BMI) (r=-0.44), vitamin A intake (r=0.23), and several FFDM unit imaging parameters, e.g. compression thickness (r=-0.34), x-ray current (r=-0.27), x-ray exposure (r=-0.18), and step-wedge x-ray attenuation curve fitting parameter B (r=-0.15). A multiple regression analysis for predicting percent breast density showed that BMI (P=0.04) and vitamin A intake (P=0.02) were significant predictors, while progesterone (P=0.18), ethnicity (P=0.40), and age (P=0.88) among others were not, controlling for FFDM variables x-ray current (P<0.001), x-ray exposure (P=0.003) and thickness (P<0.001) in the final model (R2=0.45, N=83). These results showed that BMI and vitamin A are predictors of breast density, even after controlling for several instrument variables which are also highly associated with breast density and are potential confounders that need to be taken into account during the study of factors influencing breast density. Research supported by U.S. Army MRMC under DADM17-01-1-0417, NCRR GCRC M01 RR00073, and NIH CA95545.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]