Breast Center

Information about dense breast tissue

What is Dense Breast Tissue?

Breast tissue is made up of:

  • Milk glands or lobules

  • Milk ducts and supportive/connective tissue

  • Fatty tissue

A radiologist, the doctor reading your mammogram, looks for dense and non-dense breast tissue. The term "breast tissue density" refers to how the breast tissue looks. Dense breast tissue is more fibrous or thick and less fatty. It shows up as white areas. Fatty tissue looks dark and transparent. A radiologist reports the amount of dense and non-dense breast tissue seen on your mammogram.

How will I know that I have dense breast tissue?

The density of your breasts is defined on a mammogram. You can't tell how dense your breasts are by doing a physical exam. Density may change throughout your lifetime. There is no relationship between breast size and density.

There are four categories used to standardize the reporting of breast density. The radiologist decides the categories (A, B, C, D) and includes it in your mammography report.

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What causes dense breast tissue?

In most cases, breast tissue density is determined by your genetics. Diet and lifestyle may or may not affect the breast tissue density. It is important to know that dense breast tissue may change over time. Women who are more likely to have dense breast tissue:

  • Are typically younger (for example, in their 40s and 50s)

  • Are premenopausal

  • Take combination hormone therapy to treat symptoms of menopause

How common is dense breast tissue?

Dense breast tissue is very common and normal. Approximately 40 percent to 50 percent of women have dense breast tissue (categories C and D). Only 10 percent are within the "extremely dense" group (category D).

Dense Breast Tissue and Screening for Breast Cancer

Both dense tissue and cancer appear white on a mammogram. This can make detecting breast cancer on a mammogram more difficult. It can also slightly increase the risk that cancer will not be detected when it is at a smaller size. Women with dense breast tissue have a higher risk of developing cancer, but the reason for that is unclear.

A mammogram is still the best way to detect changes in your breasts and catch cancer as early as possible. Screening mammography is important and effective in women with increased breast density. Women with dense breasts should still get mammograms. Mammography is the only proven screening method to decrease breast cancer mortality (risk of dying from breast cancer), regardless of breast density. Digital Breast Tomosynthesis (DBT), or 3-D mammograms, provide better ways to see changes on a mammogram, even in dense breast tissue.

Other tests, such as ultrasound or MRI, may detect more cancers, but can also give false positives. This means a test that at first looks positive for cancer is later found to be benign (not cancer) after more tests. Other tests may also pose other health risks. There is no evidence that these other tests are better in the long run (long-term outcomes) or prevent women from dying from cancer (improve survival rates). There are many factors that determine the need and value for more tests, including your individual risks for breast cancer. Talk to your doctor about risks and benefits of mammography and routine screenings. Learn more about our services for those who may have a higher risk for breast cancer at the PATHS (Prevention, Assessment and Tailored Health Screening) Clinic.

Wisconsin Breast Density Legislation

Wisconsin passed a law to inform people with dense breasts (categories C and D) about breast density. Breast density has always been part of the mammogram report and communicated to the ordering provider. This law ensures that the message below will be included in the letter that people receive after their mammogram if their breast density is in the two highest categories (C and D).

“Your mammogram shows that your breast tissue is dense. Dense breast tissue is found in almost 40 percent of women and is a normal finding. However, studies show that dense breast tissue can make it harder to find cancer on a mammogram and is associated with a slightly increased risk of breast cancer. Regular screening mammograms are still recommended for you. This information is provided to raise your awareness about the result of your mammogram. You can use this information to talk with your health care professional about your own risks for breast cancer. Together, you can decide which screening options are right for you. The results of your mammogram were sent to your doctor. Please note that breast density is affected by several factors and may change over time.”