Predictors of false negative axillary ultrasound in breast cancer

Background We sought to identify clinicopathologic factors related to false negative axillary ultrasound (AUS) results. Methods Patients with a clinically node-negative stage I-II breast cancer who also had a normal AUS were identified from our prospectively maintained database. All AUS studies were interpreted by dedicated breast radiologists as "normal" according to the absence of specific characteristics shown to be commonly associated with metastatic involvement. True- and false-negative AUS studies were compared statistically based on clinical, radiographic, and histologic parameters. Results Of the 118 patients with a normal AUS, 25 (21%) were ultimately found to be node-positive on pathologic assessment after axillary surgery. On bivariate analysis, primary tumor size and lymphovascular invasion (LVI) were found to be significantly different between true- and false-negative AUS. The average tumor size was smaller in the true-negative group compared with that in the false-negative group (16 versus 21 mm [P < 0.01]). The presence of LVI was more likely in the false-negative group (44%) compared with that in the true-negative group (8%, P < 0.0001). No significant difference was noted between groups with regard to patient age, race, body mass index, tumor grade, histologic type, hormone receptor status, and time between AUS and axillary surgery. On multivariate analysis, only the presence of LVI achieved statistical significance (P = 0.0007). Conclusions AUS is a valuable tool that accurately predicted absence of axillary disease in 79% of patients with clinically node-negative breast cancer. AUS findings may be less accurate in the setting of LVI, and a negative AUS in patients with LVI should be interpreted cautiously.