Mammographic Density: Potential as a Risk Factor and Surrogate Marker in the Clinical Setting

Mammographic breast density reflects the relative proportions of fat, connective, and epithelial tissue on the mammogram. Studied for over 30 years, breast density continues to be one of the strongest risk factors for all types of breast cancer. Recent evidence suggests breast density may be a useful surrogate marker for response to endocrine therapies and potentially, a marker of local recurrence as well. High density is also prevalent in the population, with 32 % of women estimated to have breasts over 50 % dense. Because of the importance and prevalence of breast density, state and federal governments have proposed or passed legislation to mandate physicians to provide information on a woman’s breast density, especially if increased. We review the evidence and clinical utility for mammographic breast density in context of breast cancer risk, outcomes, and response to therapy. Further, we describe the implications of high density for screening, and include a discussion of potential supplemental screening strategies for women with high density.