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What is BI-RADS? Understanding Your Breast Imaging Report

“Interpreting mammograms, even good ones, is considered the hardest task in radiology, requiring extensive training and specialization” as stated in a 2002 New York Times article.  The American College of Radiology (ACR) developed a breast imaging reporting system to standardize reporting, decrease ambiguity, enhance diagnostic accuracy, and improve communication with referring clinicians.  This reporting system is known as the Breast Imaging Reporting and Data System (BI-RADS), with the 5th Edition of BI-RADS released in 2013.   Use of this reporting system is required for all breast imaging studies including screening mammograms, diagnostic mammograms, breast ultrasounds, and breast MRI.

By law, letters are sent directly to patients describing the result of the screening mammogram or other breast imaging study giving a general description of the findings- ie:  normal or abnormal.  In the patient letters, the BI-RADS category is not specifically stated as this may lead to confusion if the patient is not familiar with the BI-RADS categories.  However, given the increased use of patient portals where imaging reports may be directly viewed by patients, I thought it would be useful to describe the BI-RADS categories to aid in the understanding of your mammogram or other breast imaging report.

BI-RADS is an extensive lexicon used by breast radiologists where each specific breast imaging abnormality or finding (as seen on mammography, ultrasound, or MRI) is described using established descriptors as published in the BI-RADS lexicon.   A comprehensive discussion of these descriptors is outside the scope of this article but referenced only to convey the breadth of BI-RADS and its role in breast imaging interpretation.  These descriptive terms should be used in the report when describing imaging findings which will ultimately guide the breast radiologist to determine which BI-RADS category is the best fit for final interpretation.

If you are looking at the radiologist-generated report in a patient portal (not the letter sent to you by the imaging facility), a BI-RADS category should be stated.  Every breast imaging study will be slated into one of these six BI-RADS categories.

BI-RADS 0: NEEDS ADDITIONAL IMAGING EVALUATION, or Prior Mammograms Requested for Comparison.

  • This category is almost exclusively used in screening mammography (but may occasionally be used with breast MRI if follow-up ultrasound is recommended).
  • A BI-RADS 0 designation is what prompts a “call-back”, asking the patient to return for additional imaging of an abnormality.
    • Additional imaging may be in the form of additional mammogram images and/or breast ultrasound
  • As discussed here The American Cancer Society reports:
    • About 10% of women who have a mammogram will be called back for additional imaging
    • 8-10% of these women will need a biopsy
    • 80% of the biopsies performed will have a benign, or negative result


  • This is a normal mammogram or other breast imaging study
  • There is no significant abnormality to report


  • Benign = NON-cancerous
  • This is also a negative mammogram or breast imaging result
  • A finding is present and described by the breast radiologist, however, the finding is benign as determined by using the BI-RADS lexicon descriptors for a finding. A few examples include atherosclerosis in the arteries of the breast, calcifications associated with fat necrosis (which can be seen with prior trauma or surgery), and normal lymph nodes.


  • This category is only used after a diagnostic workup is complete to further evaluate an abnormality seen on a screening mammogram resulting in a BI-RADS 0 call back.
  • There is a finding in the breast, but based on the imaging appearance of the finding, the radiologist feels that there is <2% chance the finding is cancer.
  • This category requires the patient to come back for a short interval follow-up imaging examination, typically in 6 months.
  • Follow-up interval may vary from facility to facility after the initial 6-month examination, but most facilities like to show that the finding does not change for at least 1 year, and often 2 years, before changing the category to BI-RADS 2, BENIGN.
  • If there are any suspicious changes on follow-up imaging- a biopsy should be considered.


  • This is a broad category, where the chance of cancer is estimated at between 2-94%. The finding does not look like cancer, but it could represent cancer.
  • This category should prompt a biopsy to establish a tissue diagnosis.
  • Some institutions give subcategories of 4A (low likelihood cancer), 4B (intermediate likelihood cancer), and 4C (moderate likelihood cancer), although it is not necessary for the radiologist to use these subcategories.


  • The finding looks like cancer on imaging and is estimated to have a > 95% chance of cancer.
  • This category should prompt a biopsy.
  • In the event of a benign (non-cancer) result from a biopsy, most radiologists will recommend a surgical excisional biopsy to completely evaluate the tissue given the highly suspicious appearance by imaging.


  • This category is only used in subsequent breast imaging studies after an initial diagnosis of cancer has been made.  Additional imaging is often performed to look for other possible cancers before surgery, or while patients are undergoing chemotherapy treatment before surgery to evaluate for treatment response.
  • Once a patient has undergone surgery to remove cancer- either lumpectomy or mastectomy, this category should not be used.

Although BI-RADS is much more extensive than the final categories discussed here, I hope this article clarifies the final interpretation of BI-RADS categories as stated in the radiologist-generated report for breast imaging studies.

Danielle M. Carroll, M.D. Danielle M. Carroll, M.D. Breast Imaging General Radiology

Written by Danielle Carroll, M.D.


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