A case-control study of mammographic densities in Hawaii.

Epidemiologic evidence suggests that mammographic densities are markers of breast cancer risk. This project investigated the relation between breast cancer and densities in women of Chinese, Japanese, Filipino, Native Hawaiian, and Caucasian ancestry. Mammograms from breast cancer cases and from healthy controls were compared using a computer-assisted method of mammographic density assessment. From 1991 to 1997, 935 cases of breast cancer were diagnosed at Kaiser Permanente in Hawaii; for 647 (69%) subjects, a control woman matched by ethnicity, year of mammogram, and age was identified. Conditional multiple logistic regression was applied to estimate the relative risk of developing breast cancer. Breast cancer risk was associated with percent densities and with the size of the dense areas. Women in the category with the most densities experienced a twofold risk of developing breast cancer as compared to women with the least densities. Adjustment for risk factors reduced the strength of the association. Odds ratios were of similar magnitude in Asian women as in Caucasian/Native Hawaiian women, but they were not statistically significant. The results of this study indicate that the associations of breast cancer risk with the magnitude of the dense areas and with the percent densities are of similar strength in women of different ethnicities although density levels vary by ethnicity.