Magnetic resonance imaging (MRI) evaluation of pathologic complete response (pCR) in different breast cancer subtypes after neoadjuvant chemotherapy (NAC).

Abstract

1111 Background: MRI is being used to address treatment response to NAC in breast cancer patients. However, its ability to predict pCR in histologically different tumors remains unclear. We tried to investigate the usefulness of MRI in evaluation of pCR in different breast cancer subtypes after treatment with NAC. Methods: Serial MRI studies were acquired before, during and after NAC in 75 evaluable patients. MRI interpretation included lesion size, morphology and dynamic enhanced evaluation imaging with initial and late enhancement. On the basis of the final MRI, response was determined to be a clinically complete response (CCR) when no residual tumor and no late enhancement were found. By using inmunohistochemistry and fluorescence in situ hybridization (FISH) for human epidermal growth factor receptor 2 (HER2/neu) amplification, tumors were divided into three subtypes: triple negative, HER2 positive, and estrogen receptor (ER) positive/HER2 negative. Every patient received chemotherapy with taxanes and anthracyclines and HER2 positive tumors were treated with trastuzumab. All patients received surgery. pCR was defined as no residual invasive tumor in the surgical specimen. Ductal carcinoma in situ residual disease was considered pCR. Results: 22 of 75 patients (29%) achieved a CCR on the final MRI. Of 22 patients with CCR all 22 (100%) were confirmed pathologically. 19 were pathologic complete responses and 3 showed in situ microscopic residual disease. 12 (55%) were HER2 positive tumors, 4 (18%) were triple negative tumors and 6 (27%) were ER positive/HER2 negative tumors. The negative predictive value of MRI for predicting pCR after NAC was 100%. Conclusions: Absence of both residual tumor and late enhancement in MRI predict pCR with high accuracy in triple negative, HER2 positive and ER positive/HER2 negative breast cancer after NAC.