Accuracy of MRI for estimating residual tumor size after neoadjuvant chemotherapy in locally advanced breast cancer: Relation to response patterns on MRI

Background. This study evaluated the accuracy of magnetic resonance imaging (MRI) for estimating residual tumor size after neoadjuvant chemotherapy in patients with locally advanced breast cancer and assessed whether the tumor pattern on MRI after chemotherapy influenced the accuracy of the MRI measurement of the residual tumor size. Patients and methods. Fifty patients who received neoadjuvant chemotherapy with doxorubicin and docetaxel for locally advanced breast cancer were evaluated with MRI before and after chemotherapy. We compared the residual tumor size measured by MRI with the pathologically determined size and investigated the influence of the residual tumor pattern on MRI ( shrinkage, nest or rim, and mixed) and pathologic characteristics on the accuracy of the MRI measurement. Results. The correlation coefficient between the residual tumor sizes determined by MRI and by pathology was 0.645. The MRI measurement agreed with the pathologically determined size in 36 patients (72%) and disagreed in 14 patients (28%), overestimating the size in 13 (26%) and underestimating the size in one (2%). Disagreement appeared to be more frequent in the cases showing a nest or rim pattern than in those exhibiting a shrinkage pattern, although this was not statistically significant (p = 0.119). Conclusions. MRI is an accurate method for predicting the extent of residual tumor after neoadjuvant chemotherapy; however, it may overestimate the residual disease, especially in cases showing a nest or rim tumor pattern and in those having combined lesions with ductal carcinoma in situ or multiple scattered nodules after neoadjuvant chemotherapy.