Breast Center

Information about dense breast tissue

What is Dense Breast Tissue?

Breast tissue is made up of:

  • Fibroglandular tissue: Milk ducts, lobules and connective tissue. Together these make up dense breast tissue

  • Fatty tissue

A radiologist, the doctor reading your mammogram, looks for dense fibroglandular tissue and non-dense fatty tissue. The term "breast tissue density" refers to how much dense breast tissue is present compared to the amount of fatty tissue. Dense tissue looks white on a mammogram and fatty tissue is dark. The radiologist categorizes the amount of dense breast tissue seen on your mammogram.

How will I know that I have dense breast tissue?

The density of your breasts is characterized on a mammogram. You can't tell how much dense tissue is present 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 describe breast density.

A: Almost entirely fatty
B: Scattered fibroglandular tissue
C: Heterogeneously dense
D: Extremely dense

The radiologist determines which category (A, B, C, D) of dense breast tissue is present and includes it on your mammogram report. Women with the two highest categories of breast density (categories C and D) are considered to have dense breasts.

Radiology images of the four categories of dense breast tissue

How common is dense breast tissue?

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

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.

Dense Breast Tissue and Screening for Breast Cancer

Both dense tissue and cancer appear white on a mammogram, which can make it more difficult to detect breast cancer on a mammogram when breast density is higher. Higher breast density has also been shown to slightly increase the risk of breast cancer but further research conclusions are still needed to explain why.

A mammogram is the best way to detect cancer as early as possible, even in women with dense breasts. 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) – sometimes called 3-D mammograms – improves detection of breast cancer, including in those with dense breast tissue.

There are many factors that impact your individual risk for developing breast cancer. In individuals who are at elevated risk for breast cancer due to their family history, a known genetic mutation, or history of radiation to the chest, breast MRI is often used as an additional screening test in addition to mammography to increase the detection of breast cancer.

UW Health offers evaluation at the PATHS (Prevention, Assessment and Tailored Health Screening) Clinic.

Some women who are not at high risk for breast cancer but have dense breasts will choose to have supplemental screening in addition to a mammogram to increase the possibility of detecting breast cancer since mammography is more limited in the setting of dense breast tissue. UW Health offers abbreviated breast MRI (AB-MR) as an additional test for these interested women.

Wisconsin Breast Density Legislation

Wisconsin passed a law to ensure that people with dense breasts (categories C and D) are aware of their increased breast density. Breast density has always been part of the mammogram report and communicated to the ordering provider. If a person has dense breasts, this law requires that the message below is included in the letter that people receive after their mammogram.

“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.”

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