The Impact of Breast Density on Breast Cancer Risk and Breast Screening

Whether measured by qualitative assessment of the parenchyma pattern or quantitatively by percent mammographic density, breast density is consistently a strong and independent risk factor for breast cancer (BC). Density is also a relatively common risk factor, and therefore an important contributor to BC risk at a population level. Including density (with other risk factors) in risk prediction models improves predictive accuracy; however, better standardization and/or automation of density measures will make the integration of breast density into risk assessment, and its application in tailored screening and primary prevention, more feasible. High breast density reduces screening sensitivity and is associated with risk of interval BC in screening; it is also associated with cancers that have poorer prognostic features. Non-randomized studies of adjunct ultrasound screening in women with mammography-negative dense breasts have provided evidence on incremental detection of BC with adjunct ultrasound and high false-positives but have not examined impact on clinical end-points, mortality, or balance of potential benefits versus harms.