BI-RADS classification by ACR

The BI-RADS breast classification refers to the Breast Imaging Reporting and Data System (BI-RADS) developed by the American College of Radiology (ACR) to standardize the interpretation and reporting of breast imaging test results, such as mammography, ultrasound, and magnetic resonance imaging.

The ACR BI-RADS breast classification consists of seven numerical categories ranging from 0 to 6:

• Category 0: Additional information is needed before a proper assessment can be made.

• Category 1: negative, no suspicious findings observed.

• Category 2: benign findings.

• Category 3: findings probably benign, follow-up recommended.

• Category 4: suspicious findings, biopsy recommended. (Further classified into 4A, 4B and 4C)

• Category 5: findings highly suggestive of malignancy, biopsy required.

• Category 6: breast cancer is known to be present.

The ACR's BI-RADS breast classification system enables radiologists to consistently and accurately report breast imaging findings and provides clear guidance to treating physicians on next steps for appropriate evaluation and treatment. In addition to the numerical classification, the BI-RADS breast report may also include information on breast density and the need for further evaluation.

Last updated in 2013 by the ACR

BI-RADS 0: Inconclusive

• Management: Additional imaging studies and/or comparison with previous mammograms are needed for proper monitoring of the finding under investigation.

• This means the radiologist may have observed a suspicious lesion, but it is not clearly defined. For this reason, a focused or magnified mammogram of the area of interest, or an additional ultrasound, may be necessary. Comparing the results with previous studies can also be helpful to determine if any changes have occurred over time.

BI-RADS 1: Normal breast

• Action: Continue with annual mammograms

• This means that no suspicious images were identified, the structures are normal, and there are no further comments. The study is considered negative because there are no abnormal findings.

BI-RADS 2: Benign (non-cancerous) findings

• Action: Continue with annual mammograms

• This means the study shows benign findings and no signs of cancer. The radiologist will describe in the report, for example, benign microcalcifications, simple cysts that may be intramammary lymph nodes, fibroadenomas, or other typical benign findings.

• The description of these findings helps with comparisons with future mammograms.

• The risk of cancer in these cases remains the same as in the general population.

BI-RADS 3: Findings probably benign (< 2% risk of malignancy)

• Management: Immediate evaluation with additional projections or ultrasound is recommended, and short-term follow-up, every 6 months, generally for two years, to establish whether the suspicious image remains stable over time, in size and appearance.

• Findings in this category have a very high probability (over 98%) of being benign (non-cancerous). These findings may include: solid nodules without calcium, glandular asymmetry, and pinpoint, uniform, or clustered microcalcifications.

• If the suspicious finding remains stable for at least two years, it is reclassified as BI-RADS 2 and annual monitoring continues. Otherwise, a fine-needle aspiration biopsy is evaluated to rule out a possible diagnosis of breast cancer.

• This approach helps avoid unnecessary biopsies, but if the suspicious area changes over time, it allows for early cancer diagnosis with a high probability of successful treatment.

BI-RADS 4: Suspicious abnormality; consider biopsy

• Management: In general, it is recommended to consider a biopsy to definitively characterize the findings and obtain an accurate diagnosis.

• This means there is a suspicious mammogram finding. It doesn't appear to indicate cancer, but because there is some suspicion, a breast biopsy should be performed.

• This category includes findings with varying levels of suspicion for malignancy, and is therefore divided into subcategories: BI-RADS 4A (BR4A): Low suspicion of cancer. BI-RADS 4B (BR4B): Intermediate suspicion. BI-RADS 4C (BR4C): Moderate suspicion, but not as high as in category 5.

Management: It is strongly recommended to perform a definitive biopsy and take appropriate action, e.g., surgical treatment.

BI-RADS 5: Abnormality that suggests a malignant finding

• This means the findings have the appearance of cancer and there is a high probability that it is cancer. The image may show a mass with unusual contours, irregular microcalcifications with a linear, ductal, or arborized arrangement.

• When there is a change in the breasts, it's important to confirm the presence of disease, and mammography helps detect even minimal, non-palpable lesions. The benefit of digital mammography is greatest when screenings are performed annually, as it allows for the detection of early changes in breast anatomy.

BI-RADS 6: Already proven malignant lesion

• Behavior: Taking appropriate actions

• This category is used only for mammogram findings that have already been shown to be cancerous, based on a previous biopsy. The diagnosis was already established with histology before treatment began. The mammogram is ordered to see how the cancer is responding to therapy.