Magnetic Resonance Imaging (MRI) Assessment of Residual Breast Cancer After Neoadjuvant Chemotherapy: Relevance to Tumor Subtypes and MRI Interpretation Threshold.

PURPOSE:To investigate the diagnostic performance of magnetic resonance imaging (MRI) for predicting pathologic complete response after neoadjuvant chemotherapy (NAC) depending on subtypes of breast cancer using different interpretation thresholds of MRI negativity. PATIENTS AND METHODS:A total of 353 women with breast cancer who had undergone NAC were included. Pathologic examination after complete surgical excision was the reference standard. Tumors were divided into 4 subtypes on the basis of expression of hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2). Tumor enhancement was assessed on early and late phases of MRI. MRI negativity was divided into radiologic complete response (rCR, complete absence of enhancement on both early and late phases) and near-rCR (no discernible early enhancement but observed late enhancement). RESULTS:Ninety (25.5%) of 353 patients experienced pathologic complete response. When analyzing the data of all patients, sensitivity of MRI was higher for rCR versus near-rCR (97.72% vs. 90.49%, P < .0001), whereas specificity was lower for rCR versus near-rCR (44.44% vs. 72.22%, P < .0001). Accuracy was equivalent (84.14% vs. 85.84%). In HR-HER2+ tumors, 100% sensitivity and negative predictive value were achieved by assessing early enhancement only. In HR+HER2- tumors, sensitivity of MRI was higher for rCR versus near-rCR (96.12% vs. 86.82%, P = .0005). CONCLUSION:Diagnostic performance of MRI after NAC differs in accordance with the subtypes and threshold of MRI negativity. MRI assessment with consideration of tumor subtypes is required, along with standardization of MRI interpretation criteria in the NAC setting.