Variation in mammographic breast density by race

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.

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.

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.

These racial differences in breast density generally do not conform to differences in race and age-specific breast cancer incidence rates.