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Why Is Breast Density Important?

Private: Catherine S. Giess, MD
Contributor Catherine S. Giess, MD

According to the American Cancer Society, approximately one in eight women will develop invasive breast cancer during her lifetime.

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 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.

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

The American College of Radiology estimates that 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. 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.

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

“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,” explains Dr. Catherine Giess, Chief of the Division of Breast Imaging at Brigham and Women’s Hospital.

Tari A. King, MD, Chief of Breast Surgery at Dana-Farber/Brigham and Women’s Cancer Center, discusses the four categories of breast density and what it means for a woman’s risk of developing breast cancer.

Private: Catherine S. Giess, MD
Catherine S. Giess, MD

Catherine S. Giess, MD, is Chief of the Division of Breast Imaging at Brigham and Women’s Hospital and Assistant Professor of Radiology at Harvard Medical School.

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