What does it mean to have dense breast tissue?

If a recent mammogram showed you have dense breast tissue, you may wonder what this means for your breast cancer risk. Studies show that dense breast tissue makes breast cancer screening more difficult and increases the risk of breast cancer.

A dense breast tissue diagnosis is an opportunity to review your breast cancer risk factors with your doctor and decide together whether additional screening tests are right for you.

What is dense breast tissue?

Dense breast tissue is a normal and common finding that references the appearance of breast tissue on a mammogram.

Breast tissue itself is composed of milk glands, milk ducts and supportive tissue (dense breast tissue), and fatty tissue (non-dense breast tissue). When viewed on a mammogram, women with dense breasts have more supportive tissue than fatty tissue.

On a mammogram, non-dense breast tissue appears dark and transparent. Dense breast tissue appears as a solid white area on a mammogram, making it difficult to see through.

Why does breast density matter?

Having dense breasts affects you in two ways. First, the diagnosis increases the chance that breast cancer may go undetected by a mammogram, since dense breast tissue can mask a potential cancer. Secondly, dense breasts increase your risk of breast cancer, though doctors aren’t certain why.

How do I know if I have dense breast tissue?

The radiologist who analyzes your mammogram will assess the ratio of non-dense tissue to dense tissue and assign a level of breast density. There are four levels of density:

  • Almost entirely fatty indicates that the breasts are almost completely composed of fat. About 1 in 10 women has this result.
  • Scattered areas of fibroglandular density indicates there are some scattered areas of density, but the majority of the breast tissue is non-dense. About 4 in 10 women have this result.
  • Heterogeneously dense indicates that there are some areas of non-dense tissue, but that the majority of the breast tissue is dense. About 4 in 10 women have this result.
  • Extremely dense indicates that nearly all of the breast tissue is dense. About 1 in 10 women has this result.

In general, women with breasts that are classified as heterogeneously dense or extremely dense are considered to have dense breasts. About half of women undergoing mammograms have dense breasts.

What causes dense breast tissue?

It’s not clear why some women have a lot of dense breast tissue and others do not. You may be more likely to have dense breasts if you:

  • Are younger. Breast tissue tends to become less dense as you age, though some women may have dense breast tissue at any age.
  • Take hormone therapy for menopause. Women who take combination hormone therapy to relieve signs and symptoms of menopause are more likely to have dense breasts.

What tests are recommended for dense breast cancer screening?

Following a dense breast tissue diagnosis, you and your doctor may consider additional or supplemental testing based on your other risk factors and your personal preferences.

This testing may include:

  • 3-D mammogram (breast tomosynthesis). Tomosynthesis uses X-rays to collect multiple images of the breast from several angles. The images are synthesized by a computer to form a 3-D image of the breast. Many mammogram centers are transitioning to incorporate 3-D mammograms as part of the standard mammogram technology. Advantages of 3-D mammography include the detection of subtle masses that might otherwise be obscured by overlying dense fibroglandular tissue.
  • Breast MRI. MRI uses magnets to create images of the breast. Breast MRI is recommended for women with an elevated personal risk of breast cancer (above 20%), such as those with genetic mutations that increase the risk of cancer.
  • Breast ultrasound. Ultrasound uses sound waves to analyze tissue. A diagnostic ultrasound is commonly used to investigate areas of concern discovered on a mammogram. Whole breast ultrasound may be used for screening purposes as a supplement to annual screening mammography in patients with dense breast tissue or an elevated personal risk of developing breast cancer.

If it’s time for your annual mammogram, talk to your doctor about your risks or reach out to our team about scheduling a comprehensive exam.

About the author

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Megan Fitzpatrick, MD, is a diagnostic radiologist on the medical staff at Baylor University Medical Center.

What does it mean to have dense breast tissue?