What is breast density?

Breast density is a description of the composition of breast tissue on a mammogram. All breasts are composed of fibrous and glandular tissue and fatty tissue. On a mammogram the fibrous and glandular tissue appears white and the fatty tissue appears black. A dense breast contains mostly white fibrous and glandular tissue with little fat.

Radiologists classify breast density on mammograms into four categories: almost entirely fatty, scattered areas of fibroglandular density, heterogeneously dense, and extremely dense. Women whose mammograms show heterogeneously dense or extremely dense tissue are considered to have “dense breasts”.

Image used by permission from the American College of Radiology

What is the science behind breast density?

Dense breasts are normal and common. Half of all women have dense breasts. Breast density may decrease with age, but for many women it remains the same.

Breast density in the United States:

  • 10% of women have almost entirely fatty breasts
  • 40% of women have scattered fibroglandular tissue density
  • 40% of women have heterogeneously dense breasts
  • 10% of women have extremely dense breasts
Image used by permission from the American College of Radiology

What will breast density notification look like?

All women who undergo screening mammography in Washington State will receive a letter from the facility that performed the mammogram. The letter will indicate whether or not each woman has dense breast tissue. Women with heterogeneously dense or extremely dense breast tissue are considered to have “dense breasts.”

What does breast density mean for me?

Having dense breasts may make it more difficult for doctors to spot a cancer on a mammogram. Cancerous and benign lumps appear white on a mammogram and can be masked by dense breast tissue which also appears white.

Dense breast tissue also slightly increases a woman’s risk for developing breast cancer. There are factors other than density which may place a woman at increased risk for breast cancer, including family history, chest radiation treatment and genetics. Women should discuss their family history, breast density and other risk factors with their doctor to determine if supplemental screening will be helpful.

What are the supplemental testing options?

Regardless of breast density the only medical imaging test proven to reduce breast cancer deaths is a screening mammogram. The WSRS and other groups recommend that all women have a mammogram every year starting at age 40. Women with dense breasts or other factors that increase their risk may consider supplemental screening tests described below.

Digital breast tomosynthesis (DBT), also called 3D mammography, creates image slices through the breast making some abnormalities easier to see. It looks and feels just like a mammogram and can be performed at the same time as a standard mammogram but not all facilities have this technology yet.

Ultrasound uses sound waves to create a different type of image of the breast. Some facilities offer screening breast ultrasound in addition to mammograms.

Magnetic resonance imaging (MRI) uses radio signals, magnets and contrast injected in a vein to create images of the breast. It can help find cancers that can’t be seen on mammography.

What is this all going to cost?

The State of Washington passed a bill in 2018 requiring insurance companies to cover DBT (3D mammography) the same as standard screening mammograms. The cost of any ultrasound or MRI screening tests will be variable and depend on your insurance plan and the availability of testing in your area. All screening tests may find things that are not cancer, at times leading to additional imaging or biopsy and additional costs. However, the goal of screening is to detect cancer early when it can be treated more quickly, with fewer drugs and costs, and provide the best chance for cure.

What if my insurance company says I’m not covered for this type of screening mammography? 

We recommend you notify the Washington State Office of the Insurance Commissioner (OIC)so they can determine whether a violation of the law is taking place or if perhaps the carrier or provider was not aware that the new law about coverage has taken effect.  Here’s the link to the OIC website:


You can also phone the OIC at 800-562-6900, 8 a.m. to 5 p.m., Monday – Friday.



Content of this page was prepared by:

Amy Henkel, MD and Jodi L Bailey, MD

Inland Imaging Spokane, WA

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