10% Tumor Diameter Shrinkage on the First Follow-Up Computed Tomography Predicts Clinical Outcome in Patients With Advanced Renal Cell Carcinoma Treated With Angiogenesis Inhibitors: A Follow-Up Validation Study

Background. Vascular endothelial growth factor (VEGF)targeted agents are standard therapies formetastatic renal cell carcinoma (mRCC), associated with variable tumor shrinkage. Response Evaluation Criteria in Solid Tumors (RECIST) is of limited utility in this setting, and other imaging changes are sought to reliably predict outcome early. We aim to validate 10% tumor shrinkage as the best early indicator of outcome. Methods. In this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study, 66 mRCC patients with 165 lesions on clinical trials of VEGF-targeted agents underwent thoracic and abdominal computed tomography at baseline and at first follow-up after therapy. Measurements were performed according to RECIST and tumor shrinkage of >= 10% decrease in sum of the longest diameter (-10% SLD). Correlation with time-to-treatment failure (TTF) and overall survival (OS) were compared and stratified by response to the radiologic criteria. Receiver-operating characteristics (ROC) analysis yielded the optimal threshold change in SLD, defining patients with prolonged survival. Results. More than 210% SLD significantly differentiated responders from nonresponders (median TTF 8.4 vs. 4.1 months, p = .001), whereas partial response by RECIST did not (median TTF6.9vs.5.5months in responders vs. nonresponders, p = .34). 210% SLD was also significantly predictive of OS (median OS 35.1 vs. 15.0 months in responders vs. nonresponders, p = .003). ROC curve analysis yielded -9.3% in SLD as the optimal threshold for response/no response. Conclusion. Ten percent tumor shrinkage is validated as a reliable early predictor of outcome in mRCC patients receiving VEGF-targetedtherapies andmay providea practicalmeasureto guide therapeutic decisions.