Mammographic density and breast cancer risk by family history in women of white and Asian ancestry

Purpose: Mammographic density, i.e., the radiographic appearance of the breast, is a strong predictor of breast cancer risk. To determine whether the association of breast density with breast cancer is modified by a first-degree family history of breast cancer (FHBC) in women of white and Asian ancestry, we analyzed data from four case–control studies conducted in the USA and Japan.

Methods: The study population included 1,699 breast cancer cases and 2,422 controls, of whom 45 % reported white (N = 1,849) and 40 % Asian (N = 1,633) ancestry. To standardize mammographic density assessment, a single observer re-read all mammograms using one type of interactive thresholding software. Logistic regression was applied to estimate odds ratios (OR) while adjusting for confounders.

Conclusions: These findings support the hypothesis that women with a FHBC appear to have a higher risk of breast cancer associated with percent mammographic density than women without a FHBC.

Results: Overall, 496 (12 %) of participants reported a FHBC, which was significantly associated with breast cancer risk in the adjusted model (OR 1.51; 95 % CI 1.23–1.84). There was a statistically significant interaction on a multiplicative scale between FHBC and continuous percent density (per 10 % density: p = 0.03). The OR per 10 % increase in percent density was higher among women with a FHBC (OR 1.30; 95 % CI 1.13–1.49) than among those without a FHBC (OR 1.14; 1.09–1.20). This pattern was apparent in whites and Asians. The respective ORs were 1.45 (95 % CI 1.17–1.80) versus 1.22 (95 % CI 1.14–1.32) in whites, whereas the values in Asians were only 1.24 (95 % CI 0.97–1.58) versus 1.09 (95 % CI 1.00–1.19).