P3-14-16: Molecular Phenotype and the Use of HER-2 Targeted Agents Influence the Accuracy of Breast MRI after Neoadjuvant Chemotherapy

Background: Improved understanding of factors affecting the accuracy of breast magnetic resonance imaging (MRI) after neoadjuvant systemic therapy (NST) can lead to more tailored use of MRI in deciding surgical extent after NST. Materials and Methods: We analyzed the imaging and clinicopathologic data of 463 patients who underwent NST. We aimed to investigate whether the molecular subtypes, as well as 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's correlation coefficient of 0.754 and 0.531, respectively). Multivariate analysis suggested estrogen receptor status as an independent factor influencing the MRI accuracy. In HER2−amplified tumors, the use of HER2−targeted agents was associated with less accurate MRI prediction. Dual HER2−blockade by using trastuzumab and pertuzumab resulted in lowest MRI accuracy among the patients treated with HER2−targeted agents. Conclusion: 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 less accurate MRI after NST. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-14-16.