Breast Density Assessment, Risk, and Significance in the Screening of Breast Cancer

Abstract

Every breast is composed of varying degrees of fibroglandular breast tissue and fatty tissue. Breast density reflects the amount of fibroglandular tissue present relative to the amount of fat, and may be assessed either qualitatively or quantitatively. The most common classification of breast density used clinically is the qualitative, subjective scale from the Breast Imaging Reporting and Data System 5th edition categorizing breast density using mammography as almost entirely fatty, scattered areas of fibroglandular density, heterogeneously dense, and extremely dense (D’Orsi et al. in Breast Imaging Reporting and Data System: ACR BI-RADS, 2012). The latter two categories are usually considered “dense” breasts in terms of risk assessment. Though dense breasts likely contribute as a small independent risk factor for breast cancer, dense breast tissue on mammography may also obscure an underlying cancer, making it more difficult for the cancer to be detected mammographically. Several states have now passed laws requiring patients to be notified if they have dense breasts and their potential options for supplemental screening (Freer in Radiographics 35:302–315, 2015; Are You Dense Advocacy, Inc. D.E.N.S.E. ® State Efforts in http://areyoudenseadvocacy.org/dense/, 2015). Presently, however, evidence in support of supplemental screening in women with dense breasts is limited, often leading to confusion for both patients and clinicians, especially when supplemental screening methods may not be covered by insurance companies (Freer in Radiographics 35:302–315, 2015; Slanetz et al. in N Engl J Med 372:593–595, 2015). Newer models of calculating a patient’s lifetime risk of breast cancer while incorporating breast density may prove useful in developing future supplemental screening recommendations for women with dense breasts (Warwick et al. in Breast Cancer Res 16:451, 2014). The purpose of this article is to familiarize the radiologist with how breast density is assessed, how increased breast density may diminish sensitivity of screening mammography, and which patient populations with dense breasts may benefit from supplemental screening based on risk stratification.