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Breast Density

What is breast density?


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Breasts are made up of two main types of tissue – fibroglandular tissue and fatty tissue. Fibroglandular tissue appears dense on a mammogram, while fatty tissue does not.

Most women have a mixture of both dense and non-dense (fatty) tissue in their breasts. The amount of dense tissue compared to the amount of non-dense tissue in your breast is commonly referred to as your breast density. Having any amount of dense breast tissue is normal and common. 

How do I know how much dense breast tissue I have? 
The amount of dense tissue in your breasts is measured by a radiologist using the Breast Imaging Reporting and Data System (BI-RADS). Your BI-RADS assessment can be found on your mammogram results letter. The amount of dense breast tissue increases with each letter:

Your breasts are composed almost entirely of non-dense (fatty) tissue.

Your breasts are composed of mainly non-dense (fatty) tissue, with some scattered areas of dense tissue.


Your breasts are composed of a mixture of non-dense (fatty) tissue and dense tissue.


Your breasts are composed of almost entirely dense tissue.

Your breast density can only be seen on a mammogram and is not related to the size or feel of your breasts. It varies from person to person and can decrease or change over time, particularly as you get older. 

Why is breast density important?

There are two important reasons why you should know your breast density:

  1. Research shows that the risk of breast cancer increases as the amount of dense tissue in a breast increases. However, breast density only has a small impact on your overall risk. You should not be alarmed if you have dense breast tissue, but you should speak with your health care provider about your overall breast cancer risk.

  2. Dense breast tissue can make it harder to find cancer on a mammogram. Normal dense breast tissue looks white. Breast masses or tumours also look white, so dense tissue can hide some tumours. This is why it is important to speak with your health care provider if you notice any changes in your breasts, even if you have recently had a normal mammogram.  

Image one: 10% of women have BI-RADS A - mammogram of breast with clear image of lump showing through less dense tissue. Image two: 40% of women have BI-RADS B - mammogram of breast with fairly clear image of lump showing through slightly dense tissue. Image 3 - 40% of women have BI-RADS C - mammogram of breast with hard-to-see lump in fairly desne tissue. Image 4: 10% of women have BI-RADS D - mammogram of breast with barely visible lump in very dense tissue.

Breast density: what you can do:

If I have dense breasts, do I still need a mammogram? 
Yes. A mammogram is the only screening test proven to reduce breast cancer deaths. Many cancers are seen on mammograms even if you have dense breast tissue.

Besides getting regular mammograms, what else should I do?

Everyone, regardless of age or breast density, should be familiar with the look and feel of their breasts. If you notice any changes in your breasts you should speak with your health care provider, even if you recently had a normal mammogram.


Even though dense breast tissue is a risk factor for breast cancer, having dense breast tissue on its own does not mean that you are at high risk for developing the disease in your lifetime. Breast density usually decreases with age.

While there is no sure way to prevent breast cancer you can take certain steps to reduce your breast cancer risk:

  • Maintain a healthy body weight and an active lifestyle.
  • Limit alcohol intake.
  • Breastfeed if possible.
  • Weigh the risks and benefits of hormone therapy for menopause symptoms.
More information on reducing your risk of breast cancer can be found here.
Are there additional tests available for those with dense breasts?
Currently, there is not enough scientific evidence to recommend other tests for women based on breast density alone: 

  • The evidence does show that other tests, such as breast ultrasound, may find additional cancers in women with dense breast tissue. 

  • However, breast ultrasound testing can have a high rate of false-positive results. A false-positive result is an abnormal test result that turns out to be normal after further testing (which can include biopsy or surgery). 

Speak to your health care provider to see if breast ultrasound is something to consider.

What else determines my risk for breast cancer? 

Besides breast density, there are other risk factors to consider:

  • Age – your risk increases as you age.
  • Personal history of breast cancer (ie. if you have had breast cancer).
  • History of breast cancer in a first-degree family member (mother, daughter, or sister).
  • Certain inherited gene mutations, including BRCA1 and BRCA2. 
Talk to your health care provider about your risk for breast cancer. Having this knowledge will help you in determining your next steps. 

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