Fig. 1. Clinically proven benign lesion in a 43-year-old woman.

A, B. Ultrasonography showed an 8.6×4.3-mm, oval-shaped, circumscribed, hypoechoic mass that was classified as category 3 based on BI-RADS. However, this lesion was classified as category 2 using the modified categorization by the ABCS-K developed for the MUST-BE trial because it was smaller than 10 mm and had an anterior-posterior ratio less than 0.7. This lesion was not pathologically confirmed, but was clinically proven to be benign, as it remained stable for 2 years. BI-RADS, Breast Imaging Reporting and Data System; ABCS-K, Alliance for Breast Cancer Screening in Korea; MUST-BE, Mammography and Ultrasonography Study for Breast Cancer Screening Effectiveness.