BI-RADS is a number from 0 to 6 that the radiologist writes at the end of a breast mammogram, ultrasound or MRI report to say how likely a finding is to be cancer and what the next step is [1, 2]. 1 and 2 mean there is nothing to worry about and routine screening is enough; 3 means "probably benign", with a chance of cancer of at most 2 in 100 and repeat imaging 6 months later; 4 and 5 mean a biopsy is needed [1]. 0 means the result is not yet complete and more images or a comparison with earlier images are needed [1, 2].
Key points
- BI-RADS 1 and 2 mean no cancer has been seen; continue mammograms on the usual schedule for your age [1, 2].
- BI-RADS 3 means "probably benign": out of every 100 people, at most 2 have cancer. Instead of a biopsy, the imaging is repeated 6 months later [1, 4].
- BI-RADS 4 means "suspicious", but most of the time it is not cancer; a needle biopsy is needed to be sure [1, 3].
- BI-RADS 0 is not a final result: out of every 100 women called back for more images after a mammogram, fewer than 5 have cancer [2, 7].
- The letters A to D on a mammogram report show the density of the breast tissue, not the chance that a lump is cancer [8].
What is BI-RADS?
BI-RADS is a common language created by the American College of Radiology for reporting breast imaging. The radiologist describes the findings with set terms and, at the end, writes a number from 0 to 6 that shows both the chance of cancer and the next step [1, 2]. The same numbers are used for breast mammograms, ultrasound and MRI [1].
If the report has several findings, the most suspicious one decides the final number [1]. A new version of the system was published in 2025, and the meaning of the numbers 0 to 5 did not change [1].
| BI-RADS | What it means | Chance of cancer | Next step |
|---|---|---|---|
| 0 | The result is not complete | Not yet known | More mammogram or ultrasound images, or a comparison with earlier images [1, 2] |
| 1 | Normal; nothing seen | Almost zero | Routine screening [1, 2] |
| 2 | A benign finding, such as a simple cyst [10] | Almost zero | Routine screening [1, 2] |
| 3 | Probably benign | At most 2 in 100 | Repeat imaging 6 months later [1, 2] |
| 4A | Low suspicion | More than 2 and up to 10 in 100 | Needle biopsy [1] |
| 4B | Moderate suspicion | More than 10 and up to 50 in 100 | Needle biopsy [1] |
| 4C | High suspicion | More than 50 and fewer than 95 in 100 | Needle biopsy [1] |
| 5 | Very likely cancer | 95 or more in 100 | Needle biopsy [1, 2] |
| 6 | Cancer already proven by biopsy | Proven | Follow-up with a surgeon or cancer specialist, and treatment [1] |
"Chance of cancer" means how many out of every 100 people with this result turn out to have cancer. These figures apply to all findings given this result; your own doctor knows your situation best.
What does BI-RADS 0 on a mammogram mean?
BI-RADS 0 means the radiologist cannot yet give a final result: either more mammogram or ultrasound images are needed, or today's images need to be compared with your earlier mammograms [1, 2]. After these checks, a final number from 1 to 5 is given [2].
Being called back is frightening, but most people who are called back do not have cancer [2]. In a large study in the United States, about 1 in every 9 women who had a screening mammogram was called back for more tests, and fewer than 5 in every 100 women called back had cancer [7]. Women with dense breast tissue are called back more often [8].
Whenever possible, the radiologist compares the new mammogram with earlier ones to look for changes [2]. So if you have had breast imaging before, bring the images or disc and their reports with you; sometimes this comparison is exactly what a BI-RADS 0 result needs [1, 2].
What does BI-RADS 3 on a breast ultrasound mean?
BI-RADS 3 means "probably benign": a finding that is almost always harmless, with a chance of cancer of at most 2 in every 100 [1, 4]. This number is given only after a full assessment, not from a screening mammogram alone [1, 4]. Common examples on ultrasound: a lump that looks like a typical fibroadenoma (oval, with a smooth edge and lying parallel to the skin), a cyst whose fluid looks slightly cloudy, or a cluster of very small cysts [4]. For these terms, see Hypoechoic breast mass, fibroadenoma or cyst.
Why is no biopsy done? Because the chance of cancer is very low, follow-up with imaging avoids unnecessary biopsies, and if there is a cancer it is usually found early [4, 5]:
- In a study of more than 3,000 "probably benign" findings on mammograms, about 1 in every 200 was cancer, and all of these cancers were found at a very early stage (stage 0 or 1) [5].
- In a study of more than 700 BI-RADS 3 findings on ultrasound, fewer than 1 in every 100 was cancer [6].
The usual follow-up plan: repeat imaging 6 months later, again 6 months after that (one year after the first result), and then one year later. If the finding has not changed for 2 years, it is usually regarded as benign (BI-RADS 2); if it grows or looks more suspicious, a biopsy is done [4]. Do not miss your follow-up appointments; in one study, only just over half of women had kept their appointments by 2 years [4].
What does BI-RADS 4 mean? The chance of cancer in 4A, 4B and 4C
BI-RADS 4 means the finding is "suspicious" and a biopsy is needed to find out what it is [1]. This group is very broad, so it is divided into three subgroups [1, 3]:
- 4A (low suspicion): most of these are benign; in a large study, fewer than 1 in every 10 people who had a biopsy had cancer [3].
- 4B (moderate suspicion): in the same study, about 2 in every 10 had cancer [3].
- 4C (high suspicion): about 7 in every 10 had cancer [3].
Not all radiologists give the subgroup; in the same study, only one third of BI-RADS 4 reports included one [3]. If your result says only "4", it means a biopsy is needed.
A biopsy is usually done with a needle guided by ultrasound or mammography, and a small piece of tissue is taken [9]. A biopsy does not make cancer spread: Does a biopsy make cancer spread?
What do BI-RADS 5 and 6 mean?
BI-RADS 5 means the finding is very likely to be cancer: 95 or more out of every 100 [1]. Even so, a definite diagnosis can only be made with a biopsy [1, 2].
BI-RADS 6 means a cancer has already been proven by biopsy and the imaging was done to plan or follow treatment [1, 2]. The next step is follow-up with a surgeon or cancer specialist and local treatment (most often surgery) [1]. For treatment, see Is breast cancer curable?
What do the letters A to D on a mammogram report mean? (breast density)
Separately from the BI-RADS number, a mammogram report also gives the density of the breast tissue as one of the letters A to D [8]. Density means the share of glandular and connective tissue compared with fat; it cannot be felt by hand and it is not a disease [8].
- A, almost entirely fatty: about 1 in every 10 women [8]
- B, scattered areas of dense tissue: about 4 in every 10 women [8]
- C, heterogeneously dense (may hide small lumps): about 4 in every 10 women [8]
- D, extremely dense (makes mammograms less sensitive): about 1 in every 10 women [8]
C and D count as "dense breasts", and nearly half of women aged 40 and over have them [8]. In dense breasts, a mammogram can miss cancer more easily, and the risk of breast cancer is also higher [8]. Talk to your doctor about whether an extra ultrasound or MRI is right for you; recommendations on this differ [8]. Read more: At what age should I start mammograms?
What should I do until the final result?
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If you can feel something, tell your doctor
If you can feel a lump, show it to a doctor even if the result was normal; the decision about a biopsy also depends on the examination, not only on the imaging result [9]. See I found a lump in my breast. What should I do?
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Report a new change promptly
If between follow-up visits a lump gets bigger, or you notice a change in the skin or nipple, discharge, or redness and swelling, do not wait for your next appointment; a finding that changes may be upgraded to BI-RADS 4 and need a biopsy [4]. For breast pain, see Does breast cancer hurt?
Frequently asked questions
What does BI-RADS 2 mean? Should I worry?
What does BI-RADS 1 mean?
Can BI-RADS 3 turn out to be cancer?
Does BI-RADS 4 mean I definitely have cancer?
No. BI-RADS 4 means a biopsy is needed; most BI-RADS 4 findings, especially 4A, turn out to be benign on biopsy [3].
My ultrasound and mammogram have different BI-RADS numbers; which is right?
When several tests are done together, the radiologist gives one final number, and the most suspicious finding decides it [1]. If two separate reports give different numbers, show both to your doctor so that the decision is based on the higher number.
After BI-RADS 3, what happens if nothing changes for 2 years?
A finding that stays the same for 2 years is usually regarded as benign (BI-RADS 2), and you go back to routine screening [4].
Does BI-RADS mean the same on a breast MRI?
Yes. The same numbers are used for mammograms, ultrasound and MRI, and each number means the same thing [1].
Notes for doctors (for physicians)
For physicians
Categories and likelihood of malignancy (BI-RADS v2025, unchanged from the 5th edition for categories 0-5). 0 incomplete (additional imaging or comparison with prior imaging); 1 and 2 essentially 0%; 3 more than 0% and no more than 2%, with 6-month short-interval follow-up, only after a full diagnostic evaluation and not at screening mammography; 4A more than 2% to 10%, 4B more than 10% to 50%, 4C more than 50% to less than 95%, with tissue diagnosis indicated in all; 5 95% or more; 6 biopsy-proven malignancy. v2025 changes: category 6 management reworded to "clinical follow-up; definitive local therapy (usually surgical, but not the only option)"; the "uncoupled" assessment-management principle, with the final category determined by the most suspicious finding; structured exam indications (asymptomatic screening, diagnostic workup, active breast cancer); two new ultrasound entries, "non-mass lesion" and "echogenic rind"; incorporation of the FDA density notification requirement (from 10 September 2024) [1].
Category 4 subdivisions (National Mammography Database). Of 1,309,950 diagnostic mammograms (2008-2014), 9.6% were category 4 and only 33.3% of these were subdivided (4A 55.6%, 4B 31.8%, 4C 12.6%). PPV3 for category 4 overall 21.1%; 4A 7.6%, 4B 22% and 4C 69.3%, all within the BI-RADS-specified ranges [3].
Category 3. Sickles 1991: 3,184 nonpalpable probably benign mammographic lesions with four follow-up mammograms over 3-3.5 years; 17 malignancies (PPV 0.5%), 15 detected by interval change before becoming palpable, all stage 0 or 1 [5]. ACRIN 6666 (screening ultrasound in an elevated-risk population): 745 category 3 lesions in 519 of 2,662 participants; 6 malignancies (0.8%; 95% CI 0.3%-1.7%); the authors suggest 1-year diagnostic follow-up may be appropriate for category 3 lesions at screening ultrasound [6]. Usual protocol: 6 months, 12 months (bilateral mammogram) and 24 months; after 24 months of stability, downgrade to category 2 or continue category 3 with annual imaging; adherence in one study 83.3% at 6 months, 75.9% at 12 months and 53.9% at 24 months [4]. Ultrasound examples of category 3: a classic-appearing fibroadenoma (oval, circumscribed, parallel, echogenicity less than fat, no posterior features or minimal posterior enhancement), an isolated complicated cyst and clustered microcysts [4].
Screening recall (BCSC, 1,682,504 digital screening mammograms, 2007-2013). Abnormal interpretation rate 11.6%, cancer detection rate 5.1 per 1,000, PPV1 4.4%, PPV2 25.6% and PPV3 28.6% [7].
Palpable mass (ACR 2022). Under 30, ultrasound first; a category 4 or 5 finding → diagnostic tomosynthesis or mammography and image-guided biopsy; a probably benign finding: the decision to biopsy depends on the clinical scenario [9].
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