What do BI-RADS categories mean on a mammogram report?

BI-RADS, short for Breast Imaging Reporting and Data System, is a standard way for radiologists to report mammogram findings. It uses categories 0 through 6, and each category carries a recommended next step.

• 0 — Need additional imaging. No category can be assigned yet. More pictures, or a comparison with your older mammograms, are needed first.
• 1 — Negative. Nothing abnormal was seen. Continue regular screening.
• 2 — Benign finding. Something was seen, and it is not cancer. Continue regular screening.
• 3 — Probably benign. The chance of cancer is no more than 2%. The usual advice is a follow-up mammogram in 6 months.
• 4 — Suspicious abnormality. A biopsy may be needed.
• 5 — Highly suggestive of cancer. The chance of cancer is at least 95%. A biopsy is required.
• 6 — Known cancer. A biopsy has already proven cancer, and imaging is being used before treatment begins.

What the scale is actually measuring

BI-RADS does not rate how serious a cancer is. It rates how suspicious an image looks, and it pairs that suspicion with an action. A category 6 is not worse than a category 5. It simply means the answer is already known.

That design has a purpose. Two radiologists looking at the same film should land on the same number and recommend the same next step, whatever clinic you walk into.

Category 4 has three levels

Category 4 is broad, so it is split. The three levels tell you a great deal about what your team expects.

• 4A means a low chance of cancer, more than 2% but no more than 10%.
• 4B means a moderate chance, more than 10% but no more than 50%.
• 4C means a high chance, more than 50% but less than 95%.

If your report says 4, look for the letter. A 4A and a 4C lead to the same biopsy but to very different odds.

Two categories that cause needless fear

Category 0 sounds alarming and usually is not. It often means this was your first mammogram and there is nothing to compare it against, or that overlapping tissue hid the view. As the National Cancer Institute notes, most people who are called back are not found to have breast cancer.

Category 3 also unsettles people, because waiting feels like inaction. It is not. With a 2% ceiling on the chance of cancer, an immediate biopsy would put many women through a procedure for nothing. A repeat mammogram in 6 months answers the question by looking for change, which is the more informative signal.

What to do with your report

Find the category number, and the letter if it is a 4. Ask directly what the recommended follow-up is and by when.

If you got a 0, make sure any earlier mammograms from another facility are sent over; that alone often resolves it. If you got a 3, book the 6-month appointment before you leave, since the value of that plan depends entirely on keeping it. If you got a 4 or 5, ask what kind of biopsy is planned and how soon you can have it.

Your report will also state whether your breast tissue is dense, using a separate scale from A to D. That is a different measure, and it is not part of the BI-RADS number.