Abstract P2-02-11: Evaluation of Tumor Response Using 3T Breast MRI Following Neoadjuvant Albumin-Bound Paclitaxel and Carboplatin with Bevacizumab or Trastuzumab
Authors: Mehta RS , Chen J-H , Bahri S , Carpenter P , Kuzucan A , Yu HJ , Nalcioglu O , Su M-Y. 
Published: April 2011

PURPOSE: MRI is known as the most accurate imaging modality for evaluating the extent of residual disease following neoadjuvant chemotherapy (NAC). Although in general breast MRI is done at 1.5T, 3T can provide a better signal-to-noise ratio and may be more sensitive to detect residual disease. In this study the diagnostic performance of 3T MRI for NAC response was investigated.

METHODS AND MATERIALS: In a period of 30 months, 42 NAC patients (29-83 y/o, mean 50 y/o) who received at least three MRI scans before, during and after therapy, and had surgery after completing NAC were analyzed in this study. The NAC protocol included albumin-bound paclitaxel, carboplatin and trastuzumab for HER-2 positive patients (N= 15), or bevacizumab for HER-2 negative patients (N=27). Some patients received doxorubicin and cyclophosphamide, bi-weekly for 4 cycles, as clinically indicated. Twenty-eight lesions were mass types and 14 showed non-mass-like enhancements. The residual tumor size was determined using the RECIST criteria, by measuring the longest dimension shown on MRI. When there was no enhancement (or, with a faint enhancement equal to the background normal tissue enhancement), the case was determined as complete clinical response (CCR). Pathological complete response (pCR) was defined as no residual invasive cancer cells, with or without DCIS. In cases with residual invasive cancer, the pathological size was determined as the longest dimension, either the longest dimension on H&E-stained slide or from the number of blocks (each 5 mm) where the malignant invasive tumor was detected, whichever was greater. For residual tumor showing as scattered cancer cells/nests, the longest dimension was estimated from the involved blocks.

RESULTS: MRI diagnosed 12 complete clinical response and 30 cases with residual cancers. In pathological examination, 12 were pCR (29%). Overall, comparing MRI diagnosis to pCR diagnosis, there were 27 true positive, 9 true negative, 3 false negative, and 3 false positive. The three false positive cases all had residual DCIS-so although MRI did not predict pCR it correctly diagnosed residual DCIS. The three false negative cases were all non-mass lesions, in which pathology showed scattered small cancer foci in 3, 14, and 14 cm areas, respectively. The sensitivity, specificity, and accuracy of MRI were 90%, 75%, and 86%. Overall, the correlation between MRI and pathologic size was higher for mass lesions than for non-mass-like lesions (r=0.80 vs. r=0.67), and similar between Her-2 positive and negative lesions (r=0.82 vs. r=0.84). The discrepancy between MRI and pathological size was larger for non-mass lesions than for mass lesions (0.6-14 cm vs. 0-3 cm).

CONCLUSIONS: Similar to 1.5T, high resolution 3T MRI has limitations for the non-mass-like lesions that break into small foci and scattered cells. This might be due to that small tumor foci have lowered angiogenic activity, limiting MR contrast agent uptake, thus lowering the detection rate. For mass lesions, MR residual tumor size was highly correlated with pathological size. Understanding the accuracy and limitations of 3T MRI for NAC patients may aid in designing an improved NAC protocol and a better surgical planning.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-02-11.