A BI-RADS 4 result on a mammogram or ultrasound report means the radiologist has seen something that needs a closer look with a biopsy. It does not mean you have breast cancer. In a large US database, roughly four out of five category 4 findings that were biopsied turned out to be benign. This article explains what the BI-RADS scale is, what the letters A, B and C after a 4 mean, what happens at the biopsy, and why the tiny marker placed during that biopsy can matter later on.
BI-RADS stands for Breast Imaging Reporting and Data System. It is a standard developed by the American College of Radiology so that every radiologist describes breast findings in the same words and ends the report with one number. That number, the assessment category, tells your doctor how likely the finding is to be cancer and what should happen next. The same scale is used for mammography, breast ultrasound and breast MRI, and it is used well beyond the US.
The categories run from 0 to 6. The American Cancer Society gives a plain language summary of each one.
| Category | What it means | Likelihood of cancer | Usual next step |
|---|---|---|---|
| 0 | Incomplete | Not yet known | More imaging |
| 1 | Negative | Essentially 0% | Routine screening |
| 2 | Benign finding | Essentially 0% | Routine screening |
| 3 | Probably benign | 2% or less | Short interval follow up, usually 6 months |
| 4 | Suspicious | More than 2% and less than 95% | Biopsy |
| 5 | Highly suggestive of malignancy | 95% or more | Biopsy |
| 6 | Known cancer, already proven by biopsy | Confirmed | Treatment planning |
Category 4 is the widest band on the scale. It covers every finding that is suspicious enough that a biopsy is recommended, but not so typical of cancer that it belongs in category 5. That is a range from just over 2 percent to just under 95 percent, which is why a bare "4" on its own tells you rather little about your personal odds.
The most common reasons for a category 4 are a solid mass with an irregular shape or edge, a cluster of fine calcifications with a suspicious pattern, an area where the normal tissue architecture looks pulled or distorted, or a new finding that was not there on earlier images. None of these is a diagnosis. They are reasons to take a sample.
To make the wide band more useful, radiologists can split category 4 into three subcategories for mammography and ultrasound findings. MRI reports normally give a category 4 without a letter.
Real world data line up with those ranges. In the US National Mammography Database, Elezaby and colleagues looked at more than 1.3 million diagnostic mammograms and found that biopsies of 4A findings showed cancer in 7.6 percent of cases, 4B in 22 percent and 4C in 69.3 percent. Across all category 4 findings the figure was 21.1 percent (doi: 10.1148/radiol.2017170770). The same study found that only a third of category 4 reports actually used a letter, so do not worry if yours simply says "4".
A BI-RADS 4 ultrasound result means the same thing as a BI-RADS 4 mammogram: suspicious, biopsy recommended. Ultrasound is often the second step after a screening recall, because it shows whether a mass is a simple fluid filled cyst or something solid. A solid mass with irregular margins, a shape that is taller than it is wide, or posterior shadowing is typically placed in category 4. Where a finding is visible on ultrasound, the biopsy is usually done under ultrasound guidance as well, which is quicker and more comfortable than a biopsy under mammography.
The line between 3 and 4 is the line between watching and sampling. A BI-RADS 3 finding is probably benign, with a likelihood of cancer of 2 percent or less, and the usual advice is a repeat image after about six months and then for up to two years. If a category 3 finding grows or changes in that time, it is upgraded to category 4 and biopsied. A BI-RADS 4 finding skips the waiting step, because the chance of cancer is high enough that waiting is not considered safe.
For almost everyone with a category 4 result, the next step is an image-guided needle biopsy. It is done as an outpatient procedure under local anesthetic and usually takes less than an hour from start to finish. The radiologist uses ultrasound, mammography (a stereotactic biopsy) or MRI to guide a needle to the exact spot and takes several small tissue cores. The differences between the needle types are covered in Breast Biopsy Needle Techniques, and the American Cancer Society describes what each type of biopsy feels like.
At the end of the procedure a tiny marker, often called a clip, is usually left at the biopsy site. You will not feel it. Some bruising afterwards is normal, and the signs that do need a call are explained in Hematoma After Breast Biopsy. What the pathologist then finds, how long it takes and how to read the report is explained in Breast Biopsy Results.
Most people never think about the biopsy marker again, and if the result is benign there is no reason to. But if the biopsy shows cancer, that marker quietly becomes one of the most important reference points in the whole treatment pathway.
Many category 4 findings are small, and most of them cannot be felt. The surgeon cannot find a lesion by touch once you are asleep, and after a biopsy, or after chemotherapy given before surgery, the original lesion can become even harder to see on imaging. The marker shows where the lesion was. It is how the radiologist confirms on later images that the right spot was sampled, how the surgical team plans the operation, and how the lesion is localized on the day of surgery. Why the biopsy clip is used and what it is made of is explained in Clip Marker in Breast Cancer, and the ways surgeons are guided to it are set out in Preoperative Localization in Breast Surgery.
No. It means the finding is suspicious enough that a sample is needed to know for sure. In a large US study about one in five biopsied category 4 findings was cancer, and for category 4A findings it was fewer than one in ten.
Both mean a biopsy is recommended, but the level of suspicion differs. A 4A finding has a low likelihood of cancer, between 2 and 10 percent. A 4C finding has a high likelihood, between 50 and 95 percent. 4B sits in between.
Yes, in almost all cases. Every category 4 finding, including 4A, comes with a recommendation for tissue diagnosis. Discuss it with your doctor if you have reasons to prefer a different approach, but follow up imaging alone is what category 3 is for, not category 4.
This varies by country and hospital. The biopsy is usually scheduled soon after the result. If you have not heard when it will take place, it is reasonable to call the breast clinic.
Yes, and most do. Common benign results after a category 4 biopsy include fibroadenomas, fibrocystic changes and other non cancerous conditions described by the American Cancer Society. Some results fall in between and are called high risk lesions, which may need a small operation to remove the area completely.
BI-RADS 5 is used when a finding looks typical of cancer, with a likelihood of 95 percent or more. A biopsy is still done first, because treatment planning needs a confirmed diagnosis and the tumor type.
A BI-RADS 4 result is where the pathway towards surgery begins for some patients, and the marker placed at the biopsy is where precise localization begins. Sirius Medical developed the Pintuition® system for the moment that follows when the result is cancer and the lesion cannot be felt. The Pintuition Marker® is a non radioactive, permanent magnetic marker that is cleared for long-term placement in soft tissue, so it can be placed weeks or months before surgery instead of on the morning of the operation. During surgery, GPSDetect™ technology gives the surgeon real-time distance and direction to the marker, and TargetLOC™ confirms when the probe is directly above it. The signal is not lost in blood, fluid or hematoma and cannot be deactivated by electrocautery.
In the first 200 cases at a French cancer center, reported by Ceccato and colleagues in Scientific Reports (doi: 10.1038/s41598-025-88430-5), every targeted lesion was excised and 39.5 percent of markers were placed 2 to 29 days before surgery. A Stanford comparison with an alternative wireless technique, published by Chinn and colleagues in Annals of Surgical Oncology (doi: 10.1245/s10434-025-18354-x), found a median operating time of 37 minutes versus 50 minutes. Elisabeth TweeSteden Hospital in the Netherlands has performed more than a thousand Pintuition® guided procedures.
Learn how Pintuition® can support precision, workflow efficiency and reliable excision in breast cancer surgery. Request demo or explore the clinical overview for more information.
Disclaimer
This article is intended for informational purposes only and should not be considered medical advice. Clinical decisions should always be made by qualified healthcare professionals based on individual patient needs and current guidelines.