Breast Density and Your Mammogram Report

Regular mammograms are the best way to find breast cancer early. But if your mammogram report says that you have dense breast tissue, you may be wondering what that means. Having dense breasts is very common and is not abnormal.

What is dense breast tissue?

Breasts are made up of lobules, ducts, and fatty and fibrous connective tissue.

  • Lobules produce milk and are often called glandular tissue.
  • Ducts are the tiny tubes that carry milk from the lobules to the nipple.
  • Fibrous tissue and fat give breasts their size and shape and hold the other tissues in place.

Your breasts will be seen as dense if you have a lot of fibrous or glandular tissue and not much fat in the breasts. Some women have more dense breast tissue than others. For most women, breasts become less dense with age. But in some women, there’s little change.

color illustration showing the structure of the breast (including location of areola, nipple, collecting ducts, ducts, lobules, fatty connective tissue, duct cells and lobular cells)

How do I know if I have dense breasts?

Breast density is seen only on mammograms. Some women think that because their breasts are firm, they are dense. But breast density isn’t based on how your breasts feel. It’s not related to breast size or firmness.

Radiologists are the doctors who “read” x-rays like mammograms. They check your mammogram for abnormal areas, and also look at breast density. 

Breast density categories

Radiologists use the Breast Imaging Reporting and Data System, or BI-RADS, to classify breast density into 4 categories. They go from almost all fatty tissue to extremely dense tissue with very little fat.
 

mammogram image showing a breast that is almost all fatty tissue

Breasts are almost all fatty tissue.

mammogram image showing a breast that has scattered areas of dense glandular and fibrous tissue

There are scattered areas of dense glandular and fibrous tissue.

mammogram image showing a breast where more of the breast is made of dense glandular and fibrous tissue

More of the breast is made of dense glandular and fibrous tissue (described as "heterogenously dense"). This can make it hard to see small tumors in or around the dense tissue.

mammogram image showing a breast that is extremely dense, which makes it hard to see tumors in the tissue

Breasts are extremely dense, which makes it hard to see tumors in the tissue. 

Some mammogram reports sent to women mention breast density. Your health care provider can also tell you if your mammogram shows that you have dense breasts.

In some states, women whose mammograms show heterogenously dense or extremely dense breasts must be told that they have dense breasts in the summary of the mammogram report that is sent to patients (sometimes called the lay summary).

The language used is mandated by each law, and may say something like this:

“Your mammogram shows that your breast tissue is dense. Dense breast tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer. This information about the results of your mammogram is given to you so you will be informed when you talk with your doctor. Together, you can decide which screening options are right for you. A report of your results was sent to your primary physician.”

Why is breast density important?

Women who have dense breast tissue seem to have a slightly higher risk of breast cancer compared to women with less dense breast tissue. It’s unclear at this time why dense breast tissue is linked to breast cancer risk.

We do know that dense breast tissue makes it harder for radiologists to see cancer. On mammograms, dense breast tissue looks white. Breast masses or tumors also look white, so the dense tissue can hide some tumors. In contrast, fatty tissue looks almost black. On a black background it’s easier to see a tumor that looks white. So, mammograms can be less accurate in women with dense breasts.

If I have dense breasts, do I still need mammograms?

Yes. Most breast cancers can be seen on a mammogram even in women who have dense breast tissue, so it’s still important to get regular mammograms. Mammograms can help save women’s lives.

Even if you have a normal mammogram result (regardless of how dense your breasts are), you should know how your breasts normally look and feel. Anytime there’s a change, you should report it to a health care provider right away.

Should I have any other screening tests if I have dense breast tissue?

At this time, experts do not agree what other tests, if any, women with dense breasts should get in addition to mammograms.

Studies have shown that breast ultrasound and magnetic resonance imaging (MRI) can help find some breast cancers that can’t be seen on mammograms. But MRI and ultrasound both show more findings that turn out not to be cancer. This can lead to more tests and unnecessary biopsies. And the cost of ultrasound and MRI may not be covered by insurance.

Talk to your health care provider about whether you should have other tests.

What should I do if I have dense breast tissue?

If your mammogram report says that you have dense breast tissue, talk with your provider about what this means for you. Be sure that your doctor or nurse knows your medical history and if there’s anything else in your history that increases your risk for breast cancer.

Any woman who’s already in a high-risk group (based on gene mutations, a strong family history of breast cancer, or other factors) should have an MRI along with her yearly mammogram.

To learn more about breast cancer risk factors, see Breast Cancer Risk and Prevention. To find out if you’re in a higher-risk group for breast cancer, see American Cancer Society Recommendations for the Early Detection of Breast Cancer.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

American College of Radiology. BI-RADS ATLAS – Mammography. Reporting System, 2013. Accessed at www.acr.org/~/media/ACR/Documents/PDF/QualitySafety/Resources/BIRADS/01%20Mammography/02%20%20BIRADS%20Mammography%20Reporting.pdf on August 24, 2017.

Helvie MA, Patterson SK. Chapter 11: Imaging Analysis: Mammography. In: Harris JR, Lippman ME, Morrow M, Osborne CK, eds. Diseases of the Breast. 5th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2014.

Saslow D, Boetes C, Burke W, et al. American Cancer Society guidelines for breast screening with MRI as an adjunct to mammography. CA Cancer J Clin. 2007 Mar-Apr;57(2):75-89.

Last Medical Review: September 1, 2017 Last Revised: October 9, 2017

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