The American College of Radiology (ACR) has developed a standard way of describing mammogram findings. 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 and ensures better follow up of suspicious findings. Here is 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 is 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 is 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 good chance (greater than 98%) of being benign (not cancer). The findings are not expected to change over time. But since it is not proven benign, it is helpful to see if an area of concern does change over time.
Follow-up with repeat imaging is usually done in 6 months and regularly thereafter 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 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 may 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.
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