Breast Cancer Molecular Phenotype and the Use of HER2-Targeted Agents Influence the Accuracy of Breast MRI After Neoadjuvant Chemotherapy

Objective: To investigate whether the accuracy of magnetic resonance imaging (MRI) after neoadjuvant systemic therapy (NST) is affected by molecular features of primary breast cancer and the use of human epidermal growth factor receptor 2 (HER2)-targeted agents. Background: Improved understanding of factors affecting the accuracy of breast MRI after NST can lead to more tailored use of MRI in deciding surgical extent after NST. Methods: We analyzed the imaging and clinicopathological data of 463 patients who underwent NST. We aimed to investigate whether the molecular subtypes, and the use of targeted therapies, were associated with changes in the accuracy of MRI predicting residual tumor extent. Results: The accuracy of MRI predicting the residual tumor extent was most accurate in triple-negative breast cancer and was least accurate in Luminal A subtype (Pearson correlation coefficient of 0.754 and 0.531, respectively). Multivariate analysis suggested estrogen receptor (ER) status as an independent factor influencing the MRI accuracy. In HER2-amplified tumors, the use of HER2-targeted agents was associated with a less accurate MRI prediction. Conclusions: The accuracy of MRI in predicting residual tumor extent was lowest in ER-positive tumors treated with NST. In HER2-positive tumors, the use of HER2-targeted agents resulted in a less accurate MRI after NST. These factors should be considered for deciding the extent of breast conservation after neoadjuvant chemotherapy.