Effective factors to raise diagnostic performance of breast MRI for diagnosing pathologic complete response in breast cancer patients after neoadjuvant chemotherapy

Background: Although MRI is a highly effective tool in evaluating residual disease after neoadjuvant chemotherapy (NAC), there are many reports of discordance between the response of MRI and pathology. To increase MR accuracy, additional methods, which reflect post-NAC changes, should be considered in diagnosis. Purpose: To evaluate effective methods that raise the diagnostic performance of MRI for predicting pathologic complete response (pCR) in breast cancer after neoadjuvant chemotherapy (NAC). Material and Methods: For 98 invasive breast carcinoma patients, chemotherapeutic response to MRI was evaluated for the following parameters: tumor size, tumor distribution pattern, kinetic curve analysis, and background parenchymal enhancement pattern (BPE). BPE was categorized as "minimal'', "mild'', "moderate'', or "marked'', according to the ACR BI-RADS criteria. Results: After NAC, the mean size of tumors decreased by 40% in non-pCR and by 59% in pCR groups, respectively. The sensitivity, specificity, false positive rate and false negative rate of MRI were 96% (78/81), 53% (9/17), 47% (8/17), and 4% (3/81), respectively. At pre-NAC MRI, the most common kinetic curve was delayed washout pattern (68%, 67/98); however, at post-NAC MRI the persistent pattern (55%, 47/86). Grouped lesion was the most common tumor distribution pattern on pre-NAC MRI (28%, 27/98), while on post-NAC solitary mass (40%, 34/86). The most common BPE at pre- and post-NAC MRI was mild and minimal enhancement, respectively. Conclusion: To improve the diagnostic accuracy of MRI, we should consider additional factors including: tumor distribution pattern, BPE, kinetic curve analysis, and tumor size.