When your mammogram report comes back, it almost always includes a category number from 0 to 6. This is your BI-RADS score — short for Breast Imaging Reporting and Data System. It is the standard language radiologists worldwide use to summarise what they saw and what should happen next.
BI-RADS is not a measure of how much cancer you have. It is a measure of how confident the radiologist is in the appearance of your breast tissue, and what follow-up is appropriate.
What the BI-RADS categories mean
Category 0 — Incomplete
The radiologist needs more information before they can give a final answer. This usually means a callback for extra views, an ultrasound, or comparison with old images.
A Category 0 result is the most common reason for a callback after a screening mammogram. It does not mean cancer was found — only that the available images are not enough to make a decision.
Category 1 — Negative
Nothing abnormal was seen. Your breast tissue looks normal. Continue routine screening at the interval your doctor recommends.
Category 2 — Benign
The radiologist saw something — a cyst, a calcified scar, a benign-looking mass — but is certain it is not cancer. No follow-up beyond routine screening is needed.
Like Category 1, this is a reassuring result.
Category 3 — Probably Benign
The radiologist saw something that is very likely not cancer (greater than 98% chance of being benign), but wants to confirm it stays the same. A short-interval follow-up — usually a repeat mammogram in 6 months — is recommended.
Category 3 is not a cancer diagnosis
A Category 3 result causes real anxiety because the word "probably" feels uncertain. The reality is that fewer than 2 in 100 Category 3 findings turn out to be cancer. The 6-month follow-up exists to catch that small minority early, not because the radiologist thinks you have cancer.
Category 4 — Suspicious
The finding has features that could be cancer, and a biopsy is recommended to find out for sure. Category 4 is sometimes split into:
- 4A: Low suspicion — small chance of cancer (about 2–10%).
- 4B: Moderate suspicion — moderate chance (about 10–50%).
- 4C: High suspicion — high chance, but not certain (50–95%).
Even Category 4 findings often turn out to be benign after biopsy. The biopsy is how the radiologist gets certainty.
Category 5 — Highly Suggestive of Malignancy
The finding has classic features of cancer (greater than 95% chance). A biopsy is still done to confirm and to determine the specific type, which guides treatment.
Category 6 — Known Biopsy-Proven Malignancy
This category is used after a biopsy has already confirmed cancer, and the mammogram is now part of treatment planning or response monitoring.
What do I do after I get my score?
- Category 0: Book the additional imaging the radiologist requested as soon as possible.
- Category 1 or 2: Continue routine screening on schedule.
- Category 3: Book the 6-month follow-up imaging.
- Category 4 or 5: Talk to your doctor about a biopsy. This is usually an image-guided needle biopsy and is much less invasive than people imagine.
- Category 6: Your treating team will guide next steps.
Why does my report mention breast density alongside BI-RADS?
Your radiologist also reports your breast density category (A through D) on most modern reports. Density and BI-RADS are two separate pieces of information. See our guide on dense breasts for more.
Will the BI-RADS score change between mammograms?
Yes, and that is expected. A finding that was Category 3 may move to Category 2 if it stays unchanged over 6 months. A new finding may push a previously Category 1 breast to Category 0 for callback. Comparing today's mammogram against your previous one is one of the most useful things the radiologist does, which is why you should bring old reports and images to every appointment.
What if I do not understand my report?
Ask. The radiologist's job is to make sense of the images, but the conversation about what it means for you happens with your referring doctor or a second-opinion radiologist. If you are unsure, you can also request an expert second opinion on the imaging.
Conclusion
BI-RADS is a numerical shorthand, not a diagnosis. Most reports come back Category 1, 2, or 3 — all of which are reassuring. Category 4 and 5 results are the ones that prompt a biopsy, and even most of those turn out to be benign. Understanding the scale gives you a clearer view of what your report is actually saying and what to do next.