Determinants of mammographic densities among women of Asian, Native Hawaiian, and Caucasian ancestry.

This cross-sectional study explored the relation between mammographic densities (a predictor of breast cancer risk), ethnicity, and dietary factors among women in Hawaii. Thirty-nine postmenopausal women with Japanese, Chinese, Caucasian, and Native Hawaiian ancestry who had received a screening mammogram completed a medical, reproductive, and dietary history. Using a computerized method, we determined the total and the dense area of the breast and calculated the ratio between the two. Blood lipids were measured using standard methods. For statistical analysis, we applied analysis of variance and multiple linear regression. Whereas the mean dense area of the breast was one third smaller in Asian than in Caucasian and Native Hawaiian women, the percent of the breast occupied by dense tissue in the Asian women was slightly higher than in the Caucasian/Hawaiian group, possibly a result of the Asian women's smaller breast size. The exploratory analysis indicated inverse relations of body mass index, high-density lipoprotein cholesterol (HDLC), age at menarche, and soy intake with mammographic densities, as well as direct relations of estrogen use and family history with mammographic densities. The results of this study suggest that variations in these factors may be responsible for ethnic differences in mammographic densities and in breast cancer risk.