Purpose: Because of the observed racial differences in risk of developing breast cancer, the authors conducted a study to determine the variation in breast density, a strong predictor of breast cancer risk, by race and age.
Methods: Study subjects were women enrolled in Group Health Cooperative of Puget Sound, Seattle, WA, aged 20-79 years, who had a screening mammogram between 6/1/96 and 8/1/97. Women with increased breast density (BI-RADS "heterogeneously dense" and "extremely dense") (n = 14,178) were compared to those with fatty breasts (BI-RADS "almost entirely fat" and "scattered fibroglandular tissue") (n = 14,323). Logistic regression was used with adjustment for age, parity, age at first birth, menopausal status, current use of hormone replacement therapy, and body mass index.
Results: The odds ratio (OR) for having dense breasts versus fatty breasts, comparing Asian to White women, increased from 1.2 [95% confidence interval (CI) 0.9-1.6] for women age <45 to 1.6 (95% CI 1.3-2.2) for women over 65. Conversely, the OR for Black compared to White women was highest for the women age 65 and younger (OR 1.7 (1.2-2.3), 1.3(1.0-1.7), and 1.7 (1.2-2.3) for women age <45, 46-55, and 56-65, respectively), whereas Black women over 65 had similar density as Whites. Hispanic women had similar density compared to Whites for all ages.
Conclusions: These racial differences in breast density generally do not conform to differences in race and age-specific breast cancer incidence rates.