Why is Breast Density Important?

October 31, 2016 Brigham and Women's Hospital


This image shows a negative screening mammogram of 45-year-old woman with dense breast tissue.

Approximately one in eight women will develop invasive breast cancer during her lifetime, according to the American Cancer Society (ACS). In recognition of Breast Cancer Awareness Month, we are publishing a three-part Breast Imaging Series throughout October. Today’s post, the final in our series, discusses breast density.

Breasts contain fibrous, glandular, and fatty tissue. Generally, breasts are considered dense if they contain a lot of fibrous and glandular tissue and less fat. Breast density is classified on a mammogram report in one of four ways:

  • Almost entirely fatty
  • Scattered areas of fibroglandular density
  • Heterogenously dense
  • Extremely dense

According to the American College of Radiology, 80 percent of women in the United States fall into one of the middle two categories, 10 percent have almost entirely fatty breasts, and the remaining 10 percent have extremely dense breast tissue.

Breast density is important for several reasons. Dense breast tissue may increase a woman’s chance of developing breast cancer. Also, detection of breast cancer using mammography is more difficult in women with dense breast tissue.


Whole breast ultrasound imaging of this same woman’s breast found a 5 mm invasive breast cancer (indicated by arrow), which was not visible on the mammogram performed the same day.

“Some women with dense breast tissue may benefit from additional screening tools, including breast ultrasound and breast MRI, which make it easier to identify early changes in dense breast tissue,” explains Dr. Catherine Giess, Chief of the Division of Breast Imaging at Brigham and Women’s Hospital (BWH). “It is important for a woman to discuss her individual risks of breast cancer – including breast density, family history of breast and ovarian cancer, and genetic abnormalities – with her care provider and radiologist to determine which screening tools make the most sense for her.”

The Division of Breast Imaging at Brigham and Women’s Hospital offers mammography, breast ultrasound, and breast MRI at multiple locations, including the Lee Bell Center at Brigham and Women’s Hospital in Boston, Brigham and Women’s Faulkner Hospital in Jamaica Plain, Brigham and Women’s/Mass General Health Care Center in Foxborough, and the Brigham and Women’s Health Care Center in Chestnut Hill.

-Jessica F.

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