Breast density

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.

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 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

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 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.