Breast (Chest) Density Information for Ontario Breast Screening Program Participants

About Breast (Chest) Density

• Breasts have 2 kinds of tissue:
  • Fatty tissue, which is fat that gives shape to the breasts
  • Fibroglandular tissue, also known as dense tissue, which keeps the breasts in place and helps make and carry milk to the nipple. A breast is considered dense when it has a lot of fibroglandular tissue, which looks white on a mammogram (the fatty tissue looks grey or black). Having some dense tissue is normal and very common.
• A mammogram is an X-ray image of the breast that checks for breast cancer. Higher density can make finding cancer hard because cancer and dense tissue both look white on a mammogram. It is important to have regular mammograms if you qualify to get them and to know what is normal for you.

People with higher density have a higher chance of getting breast cancer than people with lower density, but it does not mean they will get breast cancer for sure (see Breast [Chest] Density and the Chance of Getting Breast Cancer).

Reporting Breast (Chest) Density

• A reading radiologist (a doctor who specializes in medical imaging) looks at your mammogram and gives you a Breast Imaging Reporting and Data System (BI-RADS) result based on how much dense tissue they see. Your BI-RADS result is found in your Ontario Breast Screening Program (OBSP) screening mammogram report.
• BI-RADS has 4 possible types (categories): A, B, C and D. People with density type A have the lowest density, while people with density type D have the highest density. The 4 density types are described below:
  • Type A, which means the breasts are almost entirely made up of fatty tissue.
  • Type B, which means the breasts are mainly made up of fatty tissue, with some small areas of fibroglandular (dense) tissue.
  • Type C, which means the breasts have a mix of fatty and fibroglandular (dense) tissue.
  • Type D, which means the breasts are almost entirely made up of fibroglandular (dense) tissue.

How Breast (Chest) Density May Change

• Breast (chest) density may change throughout someone’s life. For example, some people may go into menopause as they get older, which causes estrogen levels to drop and can cause breasts to become more fatty and less dense.
• Some people have higher density after taking a hormone called “estrogen.”

Finding out Your Breast (Chest) Density Information

• Having a mammogram is the only way to know your breast (chest) density. You cannot tell what your density is based on the way your breasts look or feel.
• If you had a mammogram through the Ontario Breast Screening Program (OBSP), you will see your breast (chest) density result in your normal results letter.
• A doctor or nurse practitioner will get a copy of their patient’s OBSP screening mammogram report from the site where the mammogram was done.
• If you did not get a result letter from the OBSP, contact your doctor or nurse practitioner for the breast (chest) density result found in your OBSP screening mammogram report. If you do not have a doctor or nurse practitioner, you can contact your site for a copy of your OBSP screening mammogram report.
• To find out your breast (chest) density from a mammogram that was done outside the OBSP, please contact the site where you had the mammogram and they may be able to give you information.

Breast (Chest) Density and the Chance of Getting Breast Cancer

• High breast (chest) density is linked to breast cancer in 2 ways:
  • Having higher density can make it hard for doctors to see breast cancer on a mammogram because fibroglandular (dense) tissue looks the same as breast cancer on a mammogram.
  • People with higher density have a higher chance of getting breast cancer than people with lower density. The reasons for this are not well known.
• One study looked at the link between breast (chest) density and the chance of breast cancer. The study collected information on Canadians ages 50 to 69 who got a mammogram and found that people with higher breast (chest) density had a higher chance of getting breast cancer.
• Dense breasts are just one of many reasons someone’s chance of getting breast cancer could be higher.
• You cannot do much to change your breast (chest) density, but it can be affected by other things (see How Breast [Chest] Density May Change).
• To learn more about what you can do to change your chance of getting breast cancer, such as drinking less alcohol, please visit Risk factors you can change or control at mycanceriq.ca.
• To learn more about things you cannot change that could increase your chance of getting breast cancer, such as a family history of breast cancer, please visit Risk factors you can’t change or control at mycanceriq.ca.
• You can also talk to a doctor or nurse practitioner about your chance of getting breast cancer and ways to lower your chance of getting breast cancer.

How Often to Get Checked for Breast Cancer

• If your mammogram shows that you have type D density (the highest density) you will be asked to come back in 1 year for a mammogram instead of in the usual 2 years.
• If your mammogram shows that you have type A, B or C density and the Ontario Breast Screening Program (OBSP) has no other reason for you to come back in 1 year, you will be invited back to get a mammogram in 2 years. One example of why you might get invited back in 1 year instead of 2 is if you have 2 or more first-degree family members (parent, sibling, or child) assigned female at birth who had breast cancer at any age.
• If you have type D density, your doctor may offer you additional screening tests, like breast magnetic resonance imaging or a breast ultrasound. These tests can help find breast cancer in people with extremely dense breasts. Additional screening tests are not offered through the OBSP at this time.