What are BI-RADS categories?

This page was reviewed under our medical and editorial policy by

Daniel Liu, MD, Plastic and Reconstructive Surgeon

This page was reviewed on September 20, 2022.

Breast imaging tests, such as mammograms, magnetic resonance imaging (MRI) and ultrasounds, help doctors assess breast tissue for abnormalities, including the early detection of breast cancer. The test results are scored in BI-RADS (Breast Imaging Reporting and Data System) categories, which range from category 1 (not cancer) to category 6 (high likelihood of cancer). A category 0 means more tests are needed.

Mammogram reports also include four categories for breast density. The categories range from category A (little density) to category D (very dense).

How are mammograms scored?

Radiologists determine the BI-RADS category using specific criteria to assess the imaging tests. They look for:

  • Masses in the breast, with notes on size, borders and density
  • Breast density
  • Calcifications (areas of calcium build-up)
  • Asymmetry
  • Tissue lesions

How are BI-RADS categories defined, and what does that mean for follow-up care?

Each BI-RADS category, from 0 to 6, has a specific clinical meaning and suggested follow-up care. Follow-up care recommendations are based on the outcomes of previous patients with the same scores.

Category 0

Category 0 means the findings are unclear. The radiologist will need more images to determine a score. In that case, the recommended follow-up care calls for more testing, such as:

  • Conducting additional mammograms or an ultrasound to see different angles of the breast tissue
  • Looking for changes in the breast based on comparisons of current and past mammogram images

Category 1

Category 1 means the findings are negative and the breast tissue appears normal. No masses, calcifications, asymmetry or other abnormalities have been found. The breast tissue is deemed healthy.

Follow-up care calls for continued monitoring with regular mammograms.

Category 2

Category 2 means the findings are benign, which is also negative for cancer. While a mass, calcification or other abnormality may have been detected, it’s not cancerous. For instance, scar tissue or a change in the breast tissue from previous surgery may be found and is scored as noncancerous breast development.

Like category 1, follow-up care calls for continued monitoring with regular mammograms.

Category 3

Category 3 means the findings are probably benign. While a mass, calcification or other abnormality may have been found, it’s most likely not cancerous.

Follow-up care calls for another mammogram in six months to check for changes, knowing that a cancerous mass changes over time. The patient will need less frequent imaging if the mass remains stable over the next two years.

According to the American Cancer Society, fewer than 2 percent of category 3 findings develop into cancer. Some patients may seek second opinions for their category 3 scores, especially if they have higher risk factors for getting breast cancer (such as someone aged 55 or older with a family history of breast cancer).

Category 4

Category 4 means the findings suspect cancer. Category 4 has three subcategories based on the chance of cancer:

  • 4A means a low chance of cancer (2 to 10 percent).
  • 4B means a moderate chance of cancer (10 to 50 percent).
  • 4C means a high chance of cancer (50 to 95 percent).

Follow-up care calls for careful monitoring and possibly a biopsy to determine whether the abnormality is cancerous. A biopsy is a small tissue sample of the abnormality. A trained medical professional uses a hollow needle or scalpel to collect the biopsy and analyze it to determine whether it’s cancer. A biopsy may help doctors understand how the cancer behaves, what treatments may help and the grade and stage of cancer. The cancer’s stage provides a general idea of how it’ll likely progress.

The uncertainty of a category 4 mammogram score may feel stressful. Patients can discuss their feelings and concerns with their care teams. If the abnormality is diagnosed as cancer, the patient and their care team will develop a treatment plan together.

Current treatment for breast cancer typically includes some combination of surgery, radiation therapy, chemotherapy, hormone therapy, targeted drug therapy or immunotherapy. Treatment will depend on the stage and characteristics of the cancer.

Category 5

Category 5 means the findings highly suggest cancer. According to the American Cancer Society, category 5 findings have a 95 percent chance or higher of being cancerous.

Follow-up biopsy and care is strongly recommended. A biopsy will help determine whether the mass is cancerous. If cancer is confirmed, the patient and their care team will develop a treatment plan together.

Category 6

Category 6 means cancer was previously diagnosed using a biopsy.

Follow-up care calls for treatment of the cancer and mammograms to see how it responds to treatment.

BI-RADS breast density results

A mammogram report typically includes information about breast density. Breast density refers to the amount of fat and fibroglandular (fibrous and glandular) tissue in the breast.

It’s harder to see through fibroglandular tissue on a mammogram. So the more fibroglandular tissue, the denser the breast. There are four categories of breast density:

  • Category A: The least dense
  • Category B: Scattered areas of dense tissue
  • Category C: More density (heterogeneous density)
  • Category D: Extremely dense

Mammogram reports will note the breast density category. While it’s common to have areas of dense breast tissue, many states require doctors to inform women with category C or D breast density of their increased risks. Namely, it may be harder to spot changes in dense tissue with mammograms, and higher breast density is a risk factor for breast cancer.

People with family histories of breast cancer or known genetic risk factors may want to ask their doctors about additional testing options.

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