Breast density

If you have had a mammogram and been told you have dense breasts, what exactly does this mean?

Breast density is about tissue

There are different types of tissue in the breasts.

Fatty tissue is made up of fat. It helps give the breasts their shape and size.

Glandular tissue is made up of ducts and the milk glands (called lobules).

Fibrous tissue is the supportive tissue of the breast. It holds the glandular tissues in place. Along with fatty tissue, it gives the breasts their shape and size. It’s also called connective tissue.

Glandular tissue and fibrous tissue are thicker (denser) than fatty tissue. Breast density is the amount of dense tissue compared to non-dense tissue. You have dense breasts if you have more glandular tissue and fibrous tissue than fatty tissue in your breasts.

Find out more about the breasts.

Having any amount of dense breast tissue is normal

Having dense breasts is common and it’s not abnormal. You might just have more dense tissue than someone else. Or you might have less. It is common in younger women and is also found in older women who take hormone replacement therapy (HRT).

Breasts become less dense with age for most women. In some women there’s little change in their breast density as they grow older. Breast density is often inherited. Other factors that can increase or decrease breast density include:

  • age
  • having children
  • tamoxifen use
  • HRT use after menopause
  • having a low body mass index
  • drinking alcohol

Only a mammogram can reveal breast density

Breast density can only be seen on a mammogram. It can’t be found by having a healthcare professional examine your breasts or by examining your breasts yourself. Breast density is not related to the size, look or feel of your breasts.

How breast density is measured

After you have had a mammogram, the pictures of your breasts are looked at by a radiologist. Fatty tissue looks dark on a mammogram, and fibrous and glandular tissues look white.

A system called BI-RADS is used to classify breast density into 4 categories from A to D. These categories describe the amount of fatty or dense tissues found in your breasts. The amount of breast density increases from A to D.

BI-RADS A: The breast is mostly fatty tissue. About 10% of women are in this category.

BI-RADS B: The breast has a few areas of dense fibrous and glandular tissues. About 40% of women are in this category.

BI-RADS C: The breast is an almost equal mix of fatty and dense tissue. About 40% of women are in this category.

BI-RADS D: The breast is almost entirely dense tissue. About 10% of women are in this category.

Breast density and cancer

Dense breast tissue makes it harder to find cancer in the breast. Normal dense breast tissue looks white on a mammogram, and so do tumours. So dense tissue can hide tumours. This means mammograms may not be as accurate in finding tumours in women with dense breasts.

Research has also shown that breast cancer risk increases with the amount of dense breast tissue a woman has. Breast density is a small part of your overall risk – having dense breasts does not mean that you will get breast cancer. But it does mean that your risk is increased.

Find out more about risk factors for breast cancer.

If you have dense breasts, research has also shown that you are no more likely to die from breast cancer than someone who does not have dense breasts.

If you have dense breasts

If you have been told you have dense breasts after a mammogram, talk to your doctor about your risks for breast cancer and how often you should have a mammogram.

Currently there isn’t enough evidence to recommend other tests for women based only on their breast density. While research shows that other tests like a breast ultrasound or an MRI might find additional cancers in women with dense breasts, these tests can have a high rate of false-positive results (where an abnormal test turns out to be normal based on follow-up testing such as a biopsy or surgery). Other tests may also find cancers that grow slowly and may never cause problems or need treatment (this is called overdiagnosis).

It’s important for you to know your body, including knowing what looks and feels normal for your breasts. Tell your doctor if you find any changes in your breast, even if it’s between mammogram appointments.

You can also learn more about how you can reduce your risk for cancer.

Expert review and references

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

We do our best to make sure that the information we provide is accurate and reliable but cannot guarantee that it is error-free or complete.

The Canadian Cancer Society is not responsible for the quality of the information or services provided by other organizations and mentioned on, nor do we endorse any service, product, treatment or therapy.

1-888-939-3333 | | © 2024 Canadian Cancer Society