The Merriam-Webster dictionary provides three essential meanings for the word “density”: having parts that are close together; being difficult to see through; and being difficult to understand. In the case of “breast density,” it is the second meaning that applies. In 2015, two breast cancer survivors – JoAnn Pushkin and Wendie Berg – joined forces to launch an educational website, DenseBreast-info.org (DB-I), to provide information on breast density to patients and healthcare professionals. For the past seven years, DB-I has provided valuable insights for understanding breast density and its impact on early detection of breast cancer.
Breasts are made up of three tissue types: fat; lobules and glands (for milk production); and fibrous connective tissue. The relative proportion of these tissues determines the breast density which may be measured on a mammogram using the BI-RADS scale (seen below left): (A) almost entirely fatty; (B) scattered fibro-glandular density; (C) heterogeneously dense; and (D) extremely dense. These four categories are influenced by a range of factors, including age, hormone therapy, lactation, weight changes and medication.
Over 40% of women have dense breasts – categories C and D – and the connective tissue, which appears white on the mammogram, can mask a malignant tumour. This can lead to a false negative diagnosis in up to 40% of women, with potentially devastating consequences. Dense breast tissue not only reduces the effectiveness of mammography it is also a significant risk factor for developing breast cancer: the denser the breast, the higher the risk. In fact, women with extremely dense breasts have a 4-fold greater risk than women with fatty breasts.
As part of its educational outreach, DB-I has been running a series of quizzes under the headline, “In the Know with DenseBreast-info.” There have so far been four multiple-choice questions. How is a woman’s breast density determined? Breast density increases breast cancer risk: true or false? For which density categories does digital breast tomosynthesis (DBT) outperform full-field digital mammography (FFDM)? What breast screening modalities are appropriate for women with dense breasts? Questions are followed by detailed explanations.
The correct answer to the question at right is D, which means that, somewhat counter-intuitively, breast density cannot be determined by the way a breast feels. Another surprising answer is that while DBT identifies more cancers than FFDM for the first three BI-RADS categories, this is not the case for extremely dense breasts. This strongly suggests that another imaging modality such as automated breast ultrasound (ABUS) should be offered to women to minimise false negative findings. Clearly, understanding breast density is important for both patients and healthcare providers.