Relationship between breast cancer risk factors and mammographic breast density in the Fernald Community Cohort

BACKGROUND: We investigated associations of known breast cancer risk factors with breast density, a well-established and very strong predictor of breast cancer risk. METHODS: This nested case-control study included breast cancer-free women, 265 with high and 860 with low breast density. Women were required to be 40-80 years old and should have a body mass index (BMI) < 35 at the time of the index mammogram. Information on covariates was obtained from annual questionnaires. RESULTS: In the overall analysis, breast density was inversely associated with BMI at mammogram (P for trend < 0.001), and parity (P for trend = 0.02) and positively associated with alcohol consumption (ever vs never: odds ratio 2.0, 95% confidence interval 1.4-2.8). Alcohol consumption was positively associated with density, and the association was stronger in women with a family history of breast cancer (P < 0.001) and in women with hormone replacement therapy (HRT) history (P < 0.001). Parity was inversely associated with density in all subsets, except premenopausal women and women without a family history. The association of parity with density was stronger in women with HRT history (P < 0.001). CONCLUSION: The associations of alcohol and parity with breast density appear to be in reverse direction, but stronger in women with a family history of breast cancer and women who ever used HRT. British Journal of Cancer (2012) 106, 996-1003. doi: 10.1038/bjc.2012.1 www.bjcancer.com Published online 26 January 2012 (C) 2012 Cancer Research UK