Abstract: Objective To investigate the diagnostic value of second-look ultrasound （SLU） for additional breast lesions of Breast Imaging Reporting and Data System （BI-RADS） category 4 or 5 detected by MRI. Methods A total of 89 suspicious lesions of BI-RADS category 4 or 5 detected additionally by magnetic resonance imaging （MRI） were retrospectively analyzed by SLU for ultrasound imaging features and BI-RADS category. Results Of the 89 additional lesions detected by MRI, 79 lesions were detected by SLU, and the detection rate was 88.8%, including 22 （27.8%） malignant lesions. There were statistically significant differences between benign and malignant groups in the boundary and blood flow distribution of mass （P<0.05）. The area under the receiver operating characteristic （ROC） curve of SLU re-evaluation was 0.800, indicating a high accuracy in diagnosing breast cancer. Conclusion SLU can effectively detect additional BI-RADS category 4 or 5 lesions by MRI and has a high diagnostic value.

Key words: Second-look ultrasound, Breast cancer, Magnetic resonance imaging, Breast Imaging Reporting and Data System