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Once “Dense”, Always Dense?

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Wendie A. Berg, MD, PhD, FACR

Breast Cancer /

The most common reason for a change in reported breast density is due to variation in the way the radiologist interprets the mammogram rather than a true change in the breast density.  All breasts contain dense tissue and fatty tissue. A radiologist evaluates the mixture of dense and fatty tissue to determine your breast density and categorizes it into one of four categories fatty, scattered fibroglandular density, heterogeneously dense, or extremely dense (see Figure 1). A variation in interpretation by the radiologist can result in describing the dense/fat mixture as “heterogeneously dense” one year and another year as “scattered fibroglandular tissue” even though there is no true change in breast density (see Figure 2).
Figure 1. The range of density patterns on mammography is shown: A) almost entirely fatty; B) scattered fibroglandular tissue; C) heterogeneously dense, which can hide small masses; and D) extremely dense, which lowers the sensitivity of mammography. Heterogeneously dense and extremely dense breasts are considered “dense”. (Courtesy Dr. Wendie Berg)
Figure 2. There is variation in description of breast density, as illustrated by pairs of mammograms from three different patients.  Some radiologists would classify each of these mammograms as heterogeneously dense since there are portions of each where masses could be hidden by dense tissue.  Other radiologists would consider only the far right pair of images to be heterogeneously dense and the others as showing scattered fibroglandular density. (Courtesy Dr. Wendie Berg) 
Breast density, though, can vary from year to year for several reasons: 
  • When a woman is pregnant, the milk-producing glands are stimulated to grow and the breasts become denser.  It usually takes about 2-3 months after discontinuing breastfeeding for the breasts to return to “normal” so that we radiologists usually advise delaying screening mammography until the breasts have “settled down”. 
  • When a woman loses weight, there can be relative loss of the fat in the breasts, and the breasts can appear denser as a result (as the amount of fat decreases while the amount of dense glandular tissue remains the same).
  • When a woman goes through menopause, there can be first an increase in breast density due to increased hormonal fluctuations and stimulation (the “last hurrah”) just before menopause, followed by a modest decrease in breast density.  
  • Hormone supplements taken after menopause, especially combination estrogen and progesterone, can cause an increase in breast density as well as an increased risk of developing breast cancer.  
Generally breast density does decrease as a woman ages. By age, more than 50% of women in their 40s have dense breasts as do 40% of women in their 50s, 30% of women in their 60s, and 25% of women over age 70.
For a comprehensive list of questions and answers on dense breasts, visit www.DenseBreast-info.org.


About The Author
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Wendie A. Berg, MD, PhD, FACR, is Professor of Radiology at the University of Pittsburgh School of Medicine. Dr. Berg specializes in breast imaging and sees patients at Magee-Womens Hospital in Pittsburgh, PA. Dr. Berg writes and co-edits one of the leading textbooks of breast imaging, Diagnostic Imaging: Breast and has been the Principal Investigator of many important research studies in breast imaging, most notably, with support of the Avon Foundation and the National Cancer Institute, the ACRIN 6666 protocol, which evaluated screening ultrasound and screening MRI in women with dense breasts. Dr. Berg is Chief Scientific Advisor to DenseBreast-info.org

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