Prediction of Clinicopathologic Response of Breast Cancer to Primary Chemotherapy at Contrast-enhanced MR Imaging: Initial Clinical Results

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Abstract
To prospectively document changes in contrast agent kinetics in patients with primary breast cancer treated with systemic chemotherapy after one or two cycles and to determine whether kinetic measures can be used to predict final clinicopathologic response. Institutional committees on clinical research and ethics approval and patient consent were obtained. Dynamic magnetic resonance (MR) examinations were performed in 25 women with primary breast cancer before treatment and after the first (n = 21) and second (n = 15) cycle of neoadjuvant chemotherapy. Kinetic parameters (transfer constant, leakage space, and rate constant) were derived for whole tumor regions of interest. Changes in histogram distributions of pixel data (median value and range) and MR imaging-derived size were correlated with final clinical and histologic response by using nonparametric methods. Receiver operating characteristic (ROC) analysis of tumor size and transfer constant changes were used to identify patients in whom no benefit was gained from chemotherapy. After the first cycle of treatment, 12 of 14 clinical responders showed decreases in tumor size, and six of seven nonresponders showed increases or no change in tumor size (P < .001). Transfer constant changes did not differ between responders and nonresponders for either clinical or pathologic assessments. After two cycles of treatment, there were tumor size increases in five of six nonresponders compared with decreases in eight of nine responders (P < .001). Reductions in transfer constant range were also observed in responders for both clinical and pathologic assessments (P = .008 and .02, respectively). No other kinetic parameter change predicted response. Size and transfer constant range were equally accurate for predicting the absence of pathologic response after two cycles of treatment (sensitivity, specificity, and area under ROC curve were 100%, 90%, and 0.93, respectively, for size and 100%, 75%, and 0.94, respectively, for transfer constant range). Reductions in MR imaging-determined size of the primary tumor best predict clinicopathologic response of breast cancer after one cycle of neoadjuvant chemotherapy. Transfer constant and size changes are equally sensitive in the identification of patients who would gain no clinical or pathologic benefit after two cycles of treatment.