MRI Assessment of Early Tumor Response in Metastatic Renal Cell Carcinoma Patients Treated With Sorafenib

OBJECTIVE. The purpose of this study was to examine early MRI changes in renal cell carcinoma (RCC) treated with the antiangiogenic agent sorafenib and to identify MRI biomarkers of RCC response to sorafenib. MATERIALS AND METHODS. Sixteen patients with RCC were evaluated by MRI before and 3-12 weeks after commencing treatment with sorafenib. Two experienced MR radiologists, blinded to treatment status, independently graded tumor appearance on T1-weighted, T2-weighted, and gadolinium-enhanced images. The proportional odds mixed model was used to compare qualitative appearance of tumors before and after therapy. Time-to-progression was correlated with Response Evaluation Criteria in Solid Tumors (RECIST) 1.0 and MR-modified Choi criteria, incorporating changes in both tumor enhancement and size. RESULTS. After sorafenib therapy, there was a significant increase in T1 signal intensity of tumors (p < 0.0001) and a significant decrease in degree of tumor enhancement (p < 0.0001). The sum of unidimensional tumor diameters decreased significantly after therapy (p = 0.005). However, the average decrease in size at early follow-up was 13%, and all patients except one had stable disease by RECIST 1.0. Early responders defined by MR-modified Choi criteria had increased time-to-progression compared with nonresponders, whereas early RECIST evaluation did not predict clinical outcome. CONCLUSION. Decreased enhancement and T1 shortening of tumors on MRI may be useful biomarkers of RCC response to angiogenesis inhibitors. Response criteria combining early changes in size and enhancement lead to better correlation with clinical outcome compared with size decrease alone.