Characteristics, malignancy rate, and follow-up of bi-rads category 3 lesions identified at breast mr imaging: Implications for mr image interpretation and management

Purpose: To (a) evaluate the frequency of Breast Imaging Reporting and Data System (BI-RADS) category 3 assessment in screening and diagnostic breast magnetic resonance (MR) imaging, (b) review findings considered indicative of BI-RADS category 3, and (c) determine outcomes of BI-RADS category 3 lesions, including upgrades, downgrades, and malignancy rates. Materials and Methods: This retrospective study was approved by the institutional review board and compliant with HIPAA. The authors retrospectively reviewed the breast MR imaging database (2009-2011) to identify breast MR images classified as showing BI-RADS category 3 lesions. There were 9216 BI-RADS assessments in 5778 examinations (3360 women). Of the 9216 assessments, 567 (6%) in 483 women (average age, 47.2 years; median age, 47.0 years) were assigned BI-RADS category 3. In women with more than one BI-RADS category 3 lesion, the first lesion reported in the impression was used for data analysis. Outcomes data were available for 435 of the 483 women (90.1%). These women comprised the study cohort. Medical records from January 1, 2009, to May 31, 2015, were reviewed to obtain demographic characteristics and outcomes. x2 statistics and 95% exact confidence intervals (CIs) were constructed. Results: MR imaging was performed for high-risk screening in 240 of the 435 patients (55.2%) and for diagnostic purposes in 195 (44.8%). Findings included mass (n = 125, 28.7%), focus (n = 111, 25.5%), nonmass enhancement (n = 80, 18.3%), moderate or marked background parenchymal enhancement (BPE) (n = 91, 20.9%), posttreatment changes (n = 16, 3.8%), and other findings (n = 12, 2.8%). Outcomes were as follows: 339 of the 435 patients (78%) did not have evidence of malignancy at more than 24 months, 28 (6.4%) underwent mastectomy (all benign), and 68 (15.6%) had lesion upgrades, with 11 cancers (2.5%). All 11 cancers were diagnosed in women with a genetic mutation or a personal history of breast cancer. No cancer was detected in cases of moderate or marked BPE. Conclusion: Six percent of all breast MR imaging assessments were categorized as BI-RADS category 3, with a cancer rate of 2.5% (95% CI: 1.3%, 4.5%). All cancers were in women with a genetic mutation or personal history of breast cancer. Marked BPE does not necessitate a BI-RADS 3 assessment.