Reassessment and Follow-Up Results of BI-RADS Category 3 Lesions Detected on Screening Breast Ultrasound

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.