Breast density and breast cancer risk: a practical review.

New legislation in several states requiring breast density notification in all mammogram reports has increased awareness of breast density. Estimates indicate that up to 50% of women undergoing mammography will have high breast density; thus, with increased attention and high prevalence of increased breast density, it is crucial that primary care clinicians understand the implications of dense breasts and are able to provide appropriate counseling. This review provides an overview of breast density, specifically by defining breast density, exploring the association between breast density and breast cancer risk, both from masking and as an independent risk factor, and reviewing supplemental screening options as part of a larger framework for counseling patients with dense breasts.