Understanding Breast Density (BI-RADS Categories)
Updated on May 28, 2026
Breast density describes how much dense tissue versus fatty tissue is seen on a mammogram. Dense tissue is very common and normal.
There are 4 categories:
BI-RADS A — Mostly Fatty
- Breasts are made up mostly of fatty tissue.
- Mammograms work very well in this type of breast.
- Cancer is usually easier to see.
BI-RADS B — Scattered Density
- Mostly fatty tissue with some areas of dense tissue.
- This is very common.
- Mammograms still work quite well.
BI-RADS C — Heterogeneously Dense
- A mix of dense and fatty tissue, with more dense tissue present.
- Dense tissue can make it harder to see small cancers on a mammogram.
- This category is considered “dense breasts.”
BI-RADS D — Extremely Dense
- Breasts are made up mostly of dense tissue.
- Mammograms can be less accurate because both dense tissue and cancers appear white on the image.
- This category is also considered “dense breasts.”
Important Things to Know
- Dense breasts are common and normal.
- Having dense breasts slightly increases the risk of breast cancer.
- Dense tissue can sometimes hide cancers on mammograms.
- Even with a normal mammogram, you should still see your healthcare provider if you notice a new lump, skin change, nipple discharge, or other breast changes.
What Should Patients Do?
- Continue regular breast screening as recommended.
- Know your breast density if it is included in your mammogram report.
- Discuss your overall breast cancer risk with your healthcare provider, especially if you have:
- Dense breasts
- Family history of breast cancer
- Previous abnormal biopsies
- Genetic risk factors
Additional Comments
- Ideally, patients with BI-RADS C or BI-RADS D breast density would also undergo screening breast ultrasound in addition to mammography. However, in British Columbia, there are currently insufficient resources to offer screening ultrasounds routinely, and therefore they are generally not available unless there are specific breast symptoms or findings that require further investigation.
- For patients with BI-RADS C or BI-RADS D breast density, you may consider performing monthly self-breast examinations as an additional layer of screening. This is best done shortly after the end of a menstrual period, when the breasts are usually the least tender and easiest to examine.
- The goal is to become familiar with what is normal for your own breasts and armpit areas, so that you can notice any new changes. If you detect anything new or concerning, such as a lump, skin change, nipple discharge, or persistent pain, please notify your family physician.
- Be an expert of your own breasts.
For additional information visit the BC Cancer Website: