Objective: The purpose of the study was to assess the positive predictive value of mammographic features and final assessment categories described in the Breast Imaging Reporting and Data System (BI-RADS) for lesions on which biopsies have been performed.
Subjects and methods: We prospectively evaluated 492 impalpable mammographically detected lesions on which surgical biopsy (as opposed to percutaneous biopsy) was performed. Each lesion was classified according to BI-RADS descriptors for masses (margins and shape) and calcifications (morphology and distribution) and was categorized by the BI-RADS final assessment categories as category 3 ("probably benign"), category 4 ("suspicious abnormality"), or category 5 ("highly suggestive of malignancy"). Mammographic and pathologic findings were reviewed.
Results: Carcinoma was present in 225 (46%) of 492 lesions. For the 492 lesions subject to biopsy, BI-RADS final assessment categories were category 3 in eight lesions (2%), category 4 in 355 (72%), and category 5 in 129 (26%). The features with highest positive predictive value for carcinoma were spiculated margins (81%), irregular shape (73%), linear calcification morphology (81%), and segmental or linear calcification distribution (74% and 68%, respectively). Carcinoma was present in 105 (81%) of 129 category 5 lesions compared with 120 (34%) of 355 category 4 lesions (p < .001). The frequency of carcinoma was higher in category 5 than in category 4 lesions for all mammographic lesion types and all interpreting radiologists.
Conclusion: The standardized terminology of the BI-RADS lexicon allows quantification of the likelihood of carcinoma in an impalpable breast lesion. The features with highest positive predictive value--spiculated margins, irregular shape, linear morphology, and segmental or linear distribution--warrant designation of a lesion as category 5.