BI-RADS breast imaging classification

What it is

BIRADS is the Breast Imaging-Reporting and Data System Categorization. The radiologist describes the lesion and gives it a category from 0 to 6, and the higher the category the more likely the lesion is suspicious and the more evaluation it requires.

Category 0 is incomplete and needs additional imaging evaluation, or comparison with previous examinations; the likelihood of malignancy is unknown, and behind it lie an asymmetry, a mass or calcifications on screening mammography. Category 1 is negative, with no mammographic evidence of malignancy and a normal mammography. Category 2 is a benign finding, again with no mammographic evidence of malignancy: an intramammary lymph node, an oil cyst, vascular calcifications, a calcifying fibroadenoma. Categories 1 and 2 are both given as essentially 0 percent likelihood of malignancy. Category 3 is a probably benign finding at less than 2 percent likelihood of malignancy, seen as a benign-appearing solid mass or clustered calcifications, and is written elsewhere as more than 0 but 2 percent or less. Category 4 is a suspicious abnormality at 12 to 25 percent, seen as a complex or solid mass or as indeterminate clustered calcifications, and a lesion may be reported as BIRADS 4b. Category 5 is highly suggestive of malignancy at greater than 95 percent, typically a spiculated mass. Category 6 is known malignancy at 100 percent, biopsy-proven.

Category 4 is also divided by how much suspicion it carries, and that second source puts the whole of category 4 at more than 2 but less than 95 percent: 4A low suspicion, more than 2 to 10 percent; 4B moderate suspicion, more than 10 to 50 percent; and 4C high suspicion, more than 50 to less than 95 percent.