The Breast Imaging Reporting and Data System (BI-RADS)

Radiologists in the U.S. and some other countries use a system called the Breast Imaging Reporting and Data System, or BI-RADS, to report what they find on your mammogram, breast ultrasound, or breast MRI. The American College of Radiology (ACR) created this system to provide a standard way for all radiologists to categorize their findings and create a plan for follow-up care.

After you have a mammogram, breast ultrasound, or breast MRI, you should receive an easy-to-understand written report of your results. The report may or may not include specific BI-RADS scoring information — for example, it might just say something like “the results show no signs of cancer.” A separate version of the report will be sent to the doctor who ordered your mammogram. That version always includes BI-RADS scores. (You can ask for a copy of that version of the report if you want.)  

BI-RADS results fall into categories numbered 0 through 6. 

The same numbered categories are used for reporting the results of mammograms, breast ultrasounds, and breast MRIs. The recommendations for follow-up may be different, though.

Assessment: Incomplete/Need additional imaging evaluation

What it means: The radiologist needs more information before they can assign a BI-RADS score. The radiologist might, for example, need to compare the images with those from an earlier mammogram; they might request another mammogram with additional pictures taken (such as magnified views); and/or they might request that a breast ultrasound or breast MRI be performed. 

Follow-up: Additional imaging needed before a category can be assigned.

Assessment: Negative

What it means: The radiologist sees no significant or noticeable abnormality on the image.

Follow-up: Continue regular screening mammograms.

Assessment: Benign (not cancerous)

What it means: The radiologist sees something abnormal on the image, such as benign calcifications or a fibroadenoma, but rules out cancer. A non-cancerous breast abnormality is called a benign breast condition.

Follow-up: Continue regular screening mammograms

Assessment: Probably benign

What it means: There is something seen in the image that is most likely not cancerous. Additional screening is needed before the next annual mammogram so the radiologist can see if the area of concern changes.

Follow-up: Get a follow-up mammogram in six months.

Assessment: Suspicious

What it means: The radiologist sees something in the image that looks suspicious and that could turn out to be cancer.

Follow-up: You may need to get a biopsy.

Assessment: Highly suggestive of malignancy (cancer)

What it means: Something in the image looks like and probably is cancer.

Follow-up: You'll need to get a biopsy.

Assessment: Known biopsy-proven malignancy

What it means: Radiologists use this category to indicate when a biopsy has already confirmed the presence of breast cancer. Having breast imaging after a breast cancer diagnosis can help doctors track how well you're responding to treatment.

Follow-up: Continue with breast cancer treatment.

BI-RADS results also include an evaluation of your breast density, with scores on a scale from A (mostly fatty, less dense) to D (extremely dense).

Knowing whether you have dense breasts is important because people with dense breasts may be at higher-than-average risk of developing breast cancer (even if they don’t have other risk factors). Dense breast tissue can also make it harder for doctors to find breast cancers on mammograms. The only way to find out if you have dense breasts is to get a mammogram.

In 2024, a Food and Drug Administration (FDA) rule on reporting breast density findings went into effect. The rule requires all U.S. mammography facilities to include information on breast density in the mammogram reports that are sent to you and your doctor. 

If your mammogram results say that you have either “heterogeneously dense” (C) or “extremely dense” (D) breasts according to the BI-RADS scoring system (or if your report just says you have “dense breasts”), ask your doctors whether they recommend that you have other imaging tests, such as a breast MRI, regularly.

Read more about breast density.

While rare, radiologists sometimes find one area of dense breast tissue that looks different from the same area on the other breast. This is called breast asymmetry. The BI-RADS results also include information on asymmetries, if any, categorized into types. Most asymmetries are not signs of breast cancer.