Dense Breast Tissue

A Healthy You: Prevention and Screening


Breast specialists at UW Health's Breast Center can identify dense breast tissue, which is more fibrous and thick and less fatty than non-dense breast tissue, during mammogram examination.


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, who is the physician reading your mammogram, defines the amount of dense and non-dense breast tissue while examining a mammogram. Dense breast tissue, which is more fibrous or thick and less fatty, shows up as white areas, similar to how cancer may appear on a mammogram (fatty tissue appears dark and transparent).


The term "breast tissue density" refers to the appearance of breast tissue on a mammogram. The more the glands and supportive tissue, the more the tissue appears as "white" or "dense;" fatty tissue appears dark and transparent. A radiologist will determine the amount of dense and non-dense breast tissue and will include it in your mammogram report.


How will I know that I have dense breast tissue?


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


There are four categories that are used by radiologists to standardize reporting of breast density. The radiologist will determine which categories (A, B, C, D) your tissue belongs to and include it in your mammography report that is sent to your primary care provider. You will receive this information in your patient letter along with the general results from your mammogram.


Dense Breast Tissue Examples and Chart

What causes dense breast tissue?


In the majority of cases, breast tissue density is determined by your genetics. Some studies suggest that other factors like diet and life style may affect the breast tissue density, yet those are not definitive. It is important to know that dense breast tissue is not constant and 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% to 50% of women have dense breast tissue (categories C and D). But, only 10% are within the "extremely dense" group (category D).


Dense Breast Tissue and Screening for Breast Cancer


Dense tissue (which appears as white areas on the mammogram) may make detecting breast cancer on a mammogram more difficult since cancer also appears white on a mammogram. 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 also have a higher risk of developing cancer, but the reason why remains unclear.


A mammogram is still the best way to detect changes in your breasts and catch cancer as early as possible. Screening mammography is still important and effective in women with increased breast density and patients 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 3D mammograms, provide radiologists better ways to see changes on a mammogram, even in dense breast tissue. Learn more about digital breast tomosynthesis, or 3D mammograms


Additional tests, such as ultrasound or MRI, may detect more cancers, but can also generate false positives (coming for additional tests or biopsies) and can carry additional health risks. There is currently no evidence that these additional tests are better on 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 additional tests, including your individual risks for breast cancer. Talk to your doctor to learn more about risks and benefits of mammography and routine screenings. Learn more about our services for patients who may have an elevated risk for breast cancer at the PATHS (Prevention, Assessment and Tailored Health Screening) Clinic.


Wisconsin Breast Density Legislation


The state of Wisconsin recently passed legislation to inform patients 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 legislation ensures that this information will now be included in the letter that patients routinely receive after their mammogram if their breast density is in the two highest categories (C and D). If so, you will see the following paragraph in your letter:


"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."