Is Breast Magnetic Resonance Imaging an Accurate Predictor of Nodal Status After Neoadjuvant Chemotherapy?

Background: With increasing use of sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy (NAC), preoperative imaging assessment of axillary lymph nodes (ALNs) has become more important in operative planning and patient counseling. We aimed to assess if MRI is an accurate predictor of the ALN status after NAC. Methods: We used our institutional proprietary prospective database to review all patients with newly diagnosed breast cancer between August 2015 and March 2017 who received NAC, underwent post-NAC MRI, and axillary surgery. Imaging findings, axillary surgery, and histopathology results were analyzed. Results: Of 114 patients receiving NAC, 50 underwent post-NAC MRI before surgery. The mean age was 46 y; 36% were triple-negative, 26% were triple-positive, 26% were ER-positive and HER2/neu-negative, and 12% were ER-negative and Her2/neu-positive. Post-NAC MRI ALN status was normal in 35 patients, of which 30 underwent SLNB and five went directly to axillary lymph node dissection (ALND). 26 of these 35 were negative for metastasis on final pathology resulting in a negative-predictive value of 74.3%. In 15 patients with an abnormal post-NAC MRI ALN status, eight went directly to ALND and seven underwent SLNB. Eight of these 15 were positive for metastasis on final pathology resulting in a positive predictive value of 53.3%. Conclusions: Assessment of axillary imaging findings on post-NAC MRI predicts the absence of nodal disease with higher accuracy than its presence but not with adequate accuracy as surrogate for surgical pathologic evaluation of ALNs. This information is valuable in both patient counseling and axillary surgical management after NAC.