Mammographic density and hormone receptor expression in breast cancer: the Multiethnic Cohort Study

Background: It is unclear whether mammographic breast density, a strong risk factor for breast cancer, predicts subtypes of breast cancer defined by estrogen receptor (ER) and/or progesterone receptor (PR) expression. Methods: In a nested case–control study, we compared the breast density of 667 controls and 607 breast cancer cases among women of Caucasian, Japanese, and Native Hawaiian ancestry in the Hawaii component of the Multiethnic Cohort Study. A reader blinded to disease status performed computer assisted density assessment on prediagnostic mammograms. Receptor status was obtained from the statewide Hawaii Tumor Registry. Tumors were classified into ER+PR+ (n = 341), ER−PR− (n = 50), ER+PR−/ER−PR+ (n = 64), and unstaged/unknown (n = 152). Mean percent density values were computed for women with more than one mammogram. Polytomous logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) while adjusting for confounders. Results: Mean percent density was significantly greater for ER+PR+ but not for ER−PR− tumors compared to controls after adjusting for age: 37.3%, 28.9% versus 29.4%, respectively. The overall OR per 10% increase in percent density were similar for ER+PR+ and ER+PR−/ER−PR+ tumors: 1.26 (95% CI 1.17–1.36) and 1.23 (95% CI 1.07–1.42), respectively. However, percent density was not found to be a predictor for ER−PR− tumors (OR 1.00, 95% CI 0.84–1.18). The results did not differ by ethnicity, nor by menopausal status, parity, or HRT use. Conclusions: Our findings indicate that within a multiethnic population, women with higher breast density have an increased risk for ER+PR+ but not ER−PR− tumors.