Effects of mammographic density and benign breast disease on breast cancer risk (United States).

Background: Having either a history of benign breast disease, particularly atypical hyperplasia or extensive mammographic breast density, is associated with increased breast cancer risk. Previous studies have described an association between benign breast disease histology and breast density. However, whether these features measure the same risk, or are independent risk factors, has not been addressed.

Methods: This case-control study, nested within the prospective follow-up of the Breast Cancer Detection Demonstration Project, evaluated both benign histologic and mammographic density information from 347 women who later developed breast cancer and 410 age- and race-matched controls without breast cancer. Multivariate logistic regression analyses provided maximum-likelihood estimates of the odds ratios (OR) and 95% confidence intervals (CI) to evaluate the relative risk of breast cancer associated with each exposure.

Results: Adjusting for mammographic density, the OR for atypical hyperplasia was 2.1 (95% CI: 1.3-3.6), and adjusting for benign breast histology, the OR for > or = 75% density was 3.8 (95% CI: 2.0-7.2). Women with nonproliferative benign breast disease and > or = 75% density had an OR of 5.8 (95% CI: 1.8-18.6), and women with < 50% density and atypical hyperplasia had an OR of 4.1 (95% CI: 2.1-8.0).

Conclusions: In this study, both benign breast disease histology and the percentage of the breast area with mammographic density were associated with breast cancer risk. However, women with both proliferative benign breast disease and > or = 75% density were not at as high a risk of breast cancer due to the combination of effects (p = 0.002) as women with only one of these factors.