ABSTRACT Background: Magnetic Resonance Imaging (MRI) is accepted as the best exploration to predict pathological response to neoadjuvant chemotherapy (NAC) in breast cancer. Our goal is to analyze the correlation between radiological complete response (rCR) and pathological complete response (pCR), globally and according to the different tumor immunophenotypes (IF). Methods: This study included patients with clinical stage I-III who were treated with NAC at our breast cancer unit between January 2006 and December 2012. Patients underwent a baseline MRI and after NAC. The radiological response was assessed according to the RECIST version 1.1 and the pathological response according to the Miller & Payne grading system. Results: A total of 214 patients were included with a mean age of 56.3 years. Concerning clinical stage, 55.1% of the patients were classified as stage II and 40.7% as stage III. Most patients (82.7%) received NAC with anthracyclines and taxanes. Regarding the type of surgery the majority of patients (69.2%) underwent breast conserving surgery. A pCR was achieved in 18.7% patients, 52% in HER2+ tumors, 31.3% in triple-negative (TN), 28.6% in luminal-B-HER2 + , 5.4% in luminal-B-HER2- and 1,4% in luminal-A. The rCR rate was 24.9%. Table 1 reports overall results of MRI accuracy predicting pCR estimating sensitivity (Se) and specificity (Sp), as well as specific results for each immunophenotype. We have analyzed the reliability of MRI to detect complete response in breast and axillary lymph nodes independently, reporting Se of 55,8% and 69.3 % respectively (p = 0,113) and Sp of 81.3% and 41% (p Overall n 214 HER2 + n 29 Luminal A n 71 LuminalB-HER2+ n 29 LuminalB-HER2- n 37 Triple negative n 48 Se (%) 57,6 (23/40) 66,7 (10/15) 0 (0/1) 28,6 (2/7) 100 (2/2) 60 (9/15) Sp (%) 82,8 (144/174) 78,6 (11/14) 78,6 (55/70) 86,3 (19/22) 91,4 (32/35) 81,8 (27/33) Conclusions: MRI achieves Se 57.6% and Sp 82.8% predicting pCR. The values of Se are higher in TN and HER2+ tumors while the values of Sp are higher in Luminal-B and TN tumors. The Sp of MRI for detecting pCR is higher in breast than in axillary lymph nodes. Disclosure: All authors have declared no conflicts of interest.

ABSTRACT Aim: Magnetic Resonance Imaging (MRI) is accepted as the best method to predict pathological response to neoadjuvant chemotherapy (NAC) in breast cancer patients, but some studies reported differences in the efficacy of MRI to detect pathological response in axilla. The aim of the study is to evaluate the correlation between radiological and pathological response in axilla. Methods: This study included patients with clinical stage I-III who were treated with NAC at our breast cancer unit. Patients underwent a baseline MRI and after NAC. The radiological response was assessed according to the RECIST version 1.1 and the pathological response according to the Miller & Payne grading system. Results: Between January 2006 and June 2013 247 patients were included. Patient characteristics are described in table 1. Anthracyclines and taxanes were the most frequent drugs used (88.7%). Regarding the type of surgery, 69.2% of patients underwent breast conserving surgery and 85.8% underwent lymphadenectomy. A pathological complete response (pCR) was achieved in 17.4% patients, 19% in breast and 24.2% in axilla We have analyzed the ability of MRI to detect pN0 in axilla after NAQ reporting sensitivity of 76% and specificity of 24%. Patients achieving pCR in breast have a probability of 63.8% to achieve pN0 also in axilla. MRI was not able to detect pN0 in 39% of patients with initial stage cN1(FNA+) and in 66% of patients with sentinel node (SN) biopsy positive before NAQ, whose underwent lymphadenectomy (39.6% classified as A and 56.6% classified as D). Table 1 Characteristics n(247) % Median age 56 + /-12 Stage I 8 3.2 II 137 55.4 III 102 41.4 Immunophenotype Luminal A 45 18.2 Luminal B-HER2(-) 83 33.6 Luminal B-HER2(+) 32 13 Triple Negative 50 20.2 HER2(+) 30 12.1 Unknown 7 2.8 Axillary lymph node at initial stage cN1(FNA+) 109 44.1 cN1(SN+) 14 5.6 cN0 124 50.3 Conclusions: MRI achieves Se 76% and Sp 24% predicting pN0 in axilla. The probability of obtaining pN0 in axilla is higher in those patients with pCR in breast. 39% of patients with initial stage cN1 and 66% of patients with SN biopsy positive before NAQ have achieved an axillar pN0 in the lymphadenectomy. These results suggest the need to improve the detection of axillary dowstaging before surgery to avoid unnecessary lymphadenectomy. Disclosure: All authors have declared no conflicts of interest.