Breast density

This page was reviewed under our medical and editorial policy by

Daniel Liu, MD, Plastic and Reconstructive Surgeon

This page was reviewed on February 8, 2022.

If your doctor told you that you have dense breasts, you may wonder what this means. Dense breasts aren’t necessarily a cause for concern, but your doctor may want to monitor you more closely.

What is dense breast tissue?

Breasts contain three types of tissue: glandular, connective and fat. Glandular, or lobule, tissue produces milk in the breast. Connective tissue and fat give breasts their shape and size and help hold everything in the breast in place.

When you have dense breasts, it means you have lower amounts of fatty tissue and higher amounts of glandular and connective tissue. This can be seen only on a mammogram. You or your health care provider can't feel it in a physical exam.

Should I worry about dense breast tissue?

Dense breasts are very common. In fact, almost half of women over the age of 40 who have had mammograms are determined to have dense breasts.

While having dense breast tissue is not abnormal or unusual, it does make it more difficult for radiologists to observe your mammogram results. Moreover, while the link is unknown, dense breasts also put you at higher risk for breast cancer, and the denser the breasts, the higher the risk. However, this doesn't mean there is a higher chance of dying from breast cancer compared to people who have more fatty breast tissue.

What causes dense breasts?

There are several reasons why you might have dense breasts. These include:

  • Older age
  • Low body mass index (BMI)
  • If you’ve had children, are pregnant or breastfeeding
  • If you’ve taken or are taking tamoxifen, a hormone treatment for breast cancer
  • If you’ve taken hormone replacement therapy after menopause

Categories of breast density

The Breast Imaging Reporting and Data System (BI-RADS) groups breast density by type. The BI-RADS was developed by the American College of Radiology and is used to interpret mammograms.

There are four categories for breast density:

  • Category A: Your breast is almost all fatty breast tissue. This is present in 10 percent of women.
  • Category B: Fibroglandular density, both glandular and connective, is found over the entire breast. Forty percent of women will fall in this category.
  • Category C: The breasts are heterogeneously dense, meaning density is evenly distributed over all of the breasts. Forty percent of women have this. 
  • Category D: Breast tissue is very dense, which makes up 10 percent of women.

When you’re considered to have dense breasts, it means you fall into the last two categories.

Dense breasts are relatively common. In women 40 years and older, almost half have dense breasts. Your doctor should be able to share if he or she sees higher areas of density on mammograms. In some states, it's required that you be informed that you have dense breasts.

Do dense breasts require additional screening?

When you have dense breasts, it can be hard for doctors to read mammograms. The dense tissue appears as white areas, the same shade as concerning breast changes such as tumors. This means doctors have a harder time interpreting the mammogram and might miss cancer growth because it's mistaken for dense tissue. In comparison, fatty tissue shows up black on a mammogram, and therefore, white areas where there is tumor growth are easier to see.

It's not clear if there is a benefit to having additional screening tests, such as an ultrasound or an MRI, if you’re told you have dense breasts. Both of these imaging tests show details of the inside of your breast, but ultrasounds use sound waves to take the pictures and MRIs use magnets.

This lack of clear research means there is no standard that health care providers can agree on when it comes to added testing. While ultrasounds and MRIs can help diagnose breast cancer that wasn't seen on a mammogram, it also can be the opposite and may show areas that look like cancer but aren't. This can lead to unnecessary further testing, such as breast biopsies. Insurance, in some cases, won't cover additional ultrasound and/or MRI testing, and the tests can be expensive.

Clinical trials are underway to evaluate the benefit of breast cancer screenings or the use of medications to lower cancer risk when you have dense breasts.

If you find out you have dense breasts, talk with your health care provider about what next steps should be. Depending on risk factors and family history, you may need yearly MRIs along with a routine mammogram.

Learn about other possible breast cancer causes and risk factors

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