Breast density

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Breast density is not about how your breasts look or feel. You can only find out if you have dense breast tissue through mammography. Having dense breasts does not mean that you will get breast cancer – but it does mean that your risk is increased.

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. You may have more or less dense tissue than someone else. Having dense breasts is more common if you're younger, but dense breast tissue is also found in older people who take hormone replacement therapy (HRT).

Breast density is not fixed and can change over time. Breasts typically become less dense with age, but you may find there's little change in your breast density as you grow older. Breast density is often inherited. Other factors that can affect breast density include:

  • age
  • having children
  • use of tamoxifen (hormone therapy drug)
  • HRT use after menopause
  • having a low body mass index
  • drinking alcohol

How breast density is measured

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.

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

Many clinics and hospitals in Canada use the American College of Radiologists Breast Imaging Reporting and Data System (BI-RADS) to report the results of the mammogram. BI-RADS is used to classify breast density into 4 different categories from A to D. These categories describe the amount of fatty or dense tissues found in your breasts, ranging from almost all fatty tissue to dense tissue with little fat. The amount of breast density increases from A to D.

BI-RADS A: The breast is mostly fatty tissue.

BI-RADS B: The breast has a few areas of dense fibrous and glandular tissues.

BI-RADS C: The breast is an almost equal mix of fatty and dense tissue.

BI-RADS D: The breast is mostly dense tissue.

Breast density and cancer

There are 2 important things to know about 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 dense breasts.

Research has also shown that breast cancer risk increases with the amount of dense breast tissue. 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. If you have dense breasts, research has shown that you are no more likely to die from breast cancer than someone who does not have dense breasts.

Find out more about risk factors for breast cancer.

If you have dense breasts

If you have been told you have dense breasts after a mammography, talk to your healthcare provider about your risks for breast cancer. You may have a mammography more often or have the option to have more screening tests.

At this time, there is not enough evidence to recommend other tests for breast cancer screening based only on breast density. Some research shows that other tests like a breast ultrasound or an MRI might find additional cancers in people with dense breasts, but 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). Until there is more evidence, you should have the option of more screening and talk to your healthcare provider about your personal risk factors to make an informed decision that is right for you.

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

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

Expert review and references

  • Supriya Kulkarni, DMRD, DNB, DABR
  • American College of Radiology. ACR BI-RADS Atlas - Mammography II: Reporting system. 2013.
  • Provincial Health Services Authority. What is Breast Density?. Vancouver, BC: 2020:
  • American Cancer Society . Breast Density and Your Mammogram Report . 2023 :
  • Bell BM, Gossweiler M. Benign Breast Calcifications. StatPearls [Internet]. January 12, 2023:
  • Division of Cancer Prevention and Control . About Dense Breasts . Bethesda, MA : Centers for Disease Control and Prevention (CDC) ; 2023:
  • . Understanding Breast Calcifications . 2024 :

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.

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