The diagnostic contribution of magnetic resonance imaging in the detection of axillary metastasis after neoadjuvant chemotherapy.

Sentinel lymph node dissection (SLND) is a reliable method that provides axillary staging in clinical node-negative (cN0) breast cancer patients before neoadjuvant chemotherapy (NACT). However, it is not a standard method on its own due to the high false-negative rates (FNR) reported in initially clinical node-positive patients (cN1-cN3). The contribution of magnetic resonance imaging (MRI) to SLND after chemotherapy is not well understood. In our study, we aimed to investigate the contribution of post-NACT MRI to SLND in breast cancer patients receiving NACT. Between January 2014 and December 2020, patients who had MRI images including the axilla after NACT and had axillary lymph nodes evaluation performed simultaneously with SLND were included in the study. MRI images of all patients were re-evaluated by 2 experienced clinicians. MRI and SLND results were analyzed to detect axillary lymph node metastasis. 117 patients were included in the study. The median age of the patients was 49 years. Before chemotherapy, 108 patients (92.3%) had tumor metastases in their axilla pathologically confirmed by tru-cut biopsy. Axillary downstage was obtained in 48.1% (n=52) of the patients after NACT. Of the 56 patients with axillary node positivity, 3 patients had no metastasis in the SLND evaluation (FNR=5.4%). The sensitivity of post-NACT MRI in detecting node positivity was 69.6%, the specificity was 90.2%, the positive predictive value (PPV) was 86.7% and the negative predictive value (NPV) was 76.4. SLND together with MRI predicted all node-positive patients (FNR=0%). In summary, SLND may not detect a group of patients with residual axillary lymph node metastases after NACT. We have shown that MRI can contribute to identifying these patients. If no metastases are detected by both methods (SLND and MRI), avoidance of axillary dissection may be an acceptable choice.