Mammograms and Other Breast Imaging Tests

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Understanding your mammogram report – BI-RADS categories

The American College of Radiology (ACR) came up with a standard way to describe mammogram findings and results. In this system, the results are sorted into categories numbered 0 through 6. This system is called the Breast Imaging Reporting and Data System (BI-RADS). Having a standard way of reporting mammogram results lets doctors use the same words and terms, which can help ensure better follow up of suspicious findings. Here’s a brief review of what the categories mean:

X-ray assessment is incomplete

Category 0: Additional imaging evaluation and/or comparison to prior mammograms is needed.

This means a possible abnormality may not be clearly seen or defined and more tests are needed, such as the use of spot compression (applying compression to a smaller area when doing the mammogram), magnified views, special mammogram views, or ultrasound.

This also suggests that the mammogram should be compared with older ones to see if there have been changes in the area over time.

X-ray assessment is complete

Category 1: Negative

There’s no significant abnormality to report. The breasts look the same (they are symmetrical) with no masses (lumps), distorted structures, or suspicious calcifications. In this case, negative means nothing bad was found.

Category 2: Benign (non-cancerous) finding

This is also a negative mammogram result (there’s no sign of cancer), but the reporting doctor chooses to describe a finding known to be benign, such as benign calcifications, lymph nodes in the breast, or calcified fibroadenomas. This ensures that others who look at the mammogram will not misinterpret the benign finding as suspicious. This finding is recorded in the mammogram report to help when comparing to future mammograms.

Category 3: Probably benign finding – Follow-up in a short time frame is suggested

The findings in this category have a very high chance (greater than 98%) of being benign (not cancer). The findings are not expected to change over time. But since it’s not proven benign, it’s helpful to see if the area in question does change over time.

Follow-up with repeat imaging is usually done in 6 months and regularly after that until the finding is known to be stable (usually at least 2 years). This approach helps avoid unnecessary biopsies, but if the area does change over time, it still allows for early diagnosis.

Category 4: Suspicious abnormality – Biopsy should be considered

Findings do not definitely look like cancer but could be cancer. The radiologist is concerned enough to recommend a biopsy. The findings in this category can have a wide range of suspicion levels. For this reason, some doctors divide this category further:

  • 4A: finding with a low suspicion of being cancer
  • 4B: finding with an intermediate suspicion of being cancer
  • 4C: finding of moderate concern of being cancer, but not as high as Category 5

Not all doctors use these subcategories.

Category 5: Highly suggestive of malignancy – Appropriate action should be taken

The findings look like cancer and have a high chance (at least 95%) of being cancer. Biopsy is very strongly recommended.

Category 6: Known biopsy-proven malignancy – Appropriate action should be taken

This category is only used for findings on a mammogram that have already been shown to be cancer by a previous biopsy. Mammograms may be used in this way to see how well the cancer is responding to treatment.

BI-RADS reporting for breast density

Mammogram reports will also include an assessment of breast density. BI-RADS classifies breast density into 4 groups:

The breasts are almost entirely fatty

The breasts contain little fibrous and glandular tissue, which means the mammogram would likely detect anything abnormal.

There are scattered areas of fibroglandular density

There are a few areas of fibrous and glandular tissue in the breast.

The breasts are heterogeneously dense, which may obscure small masses

The breast has more areas of fibrous and glandular tissue that are found throughout the breast. This can make it hard to see small masses.

The breasts are extremely dense, which lowers the sensitivity of mammography

The breast has a lot of fibrous and glandular tissue. This can lead to missing some cancers.

In some states, women whose mammograms show heterogeneously dense or extremely dense breasts must be told that they have “dense breasts” in the summary of the mammogram report that is sent to patients (sometimes called the lay summary). The language used is mandated by law, and may say something like, “Your mammogram shows that your breast tissue is dense. Dense breast tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer. This information about the results of your mammogram is given to you to raise your awareness and to inform your conversations with your doctor. Together, you can decide which screening options are right for you. A report of your results was sent to your physician.”


Last Medical Review: 12/10/2013
Last Revised: 06/10/2014