Objective: The purpose of this study is to determine the frequency and the malignancy rate of BI-RADS category 3 lesions detected on screening breast ultrasound and to reassess whether they satisfied the requirements of the American College of Radiology Imaging Network (ACRIN) 6666 protocol.
Materials and methods: Of 28,796 asymptomatic women who underwent screening mammography during 2 years, 12,187 underwent additional ultrasound as part of the screening. Patients for whom BI-RADS category 3 lesions were seen on the ultrasound were selected. We reviewed the initial ultrasound showing BI-RADS category 3 lesions and mammograms. We also investigated the clinical outcome of these lesions using the reference standard of a combination of pathologic analysis and follow-up for at least 24 months.
Results: The frequency of BI-RADS category 3 lesions detected on screening ultrasound was 14.6% (1783/12,187). Of the 1164 patients with a follow-up duration of at least 24 months or whose lesions were biopsied, eight were eventually proven to have malignancy (0.7%). The malignancy rate was 2.2% (4/184) for patients with abnormal mammograms and 0.4% (4/980) for those with normal mammograms. When the ACRIN 6666 protocols were strictly applied, 225 (19.3%) lesions were retrospectively recategorized as BI-RADS category 4 (n = 12) or category 2 (n = 213). All detected malignancies were early breast cancers with no lymph node metastasis.
Conclusion: Although the frequency of ultrasound BI-RADS category 3 lesions is considerably high (14.6%), the malignancy rate is very low (0.7%), especially in patients with a normal mammogram. Therefore, with BI-RADS category 3 assessment, careful evaluation is required to avoid unnecessary short-interval follow-up or biopsy.
Keywords: BI-RADS; breast neoplasm; probably benign lesion; ultrasound.