Background: It is assumed that axillary ultrasound (AxUS) is the best method for axillary nodal evaluation in newly diagnosed breast cancer patients. However, few have evaluated the efficacy of preoperative axillary MRI. We compared the statistical accuracy of AxUS and MRI in detecting nodal metastases among breast cancer patients who were selected for neoadjuvant chemotherapy. Study Design: We retrospectively analyzed 219 breast cancer patients undergoing neoadjuvant chemotherapy from 2007 to 2015, all of whom had AxUS and breast MRI before chemotherapy. Two breast radiologists, blinded to clinical, pathologic, and AxUS findings, re-reviewed all breast MRIs, specifically focusing on axillary nodal characteristics. We correlated clinico-pathologic characteristics, AxUS, and MRI findings, and quantified predictive values of both imaging modalities. Results: Overall, 101 of 219 (47%) patients had T2 tumors. The most common abnormal nodal finding was size >10 mm. Axillary ultrasound and MRI agreed on nodal status in 192 of 219 patients (87.6%). When correlated with pre-chemotherapy needle biopsy in 129 patients, AxUS and axillary MRI performed similarly (sensitivity of 99.1% vs 97.4% and specificity 15.4% vs 15.4%, respectively). Only 4 of 129 (3.1%) patients had a negative MRI and positive AxUS; 3 of 4 of these patients (75%) had a positive biopsy and 2 of 3 had positive lymph nodes on final pathology, therefore suggesting MRI missed clinically significant disease in only 2 of 129 (1.5%) patients. Conclusions: In a high-risk patient population, AxUS and MRI have similar statistical profiles in evaluating axillary nodal status. Routine use of AxUS after a normal axillary MRI is not warranted.
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