The Radiographic Interpretation of Response to Avastin in Glioblastoma Multiforme

Avastin generates a decrease in vascular permeability in GBM which is marked by a decrease in cerebral edema and a decrease in contrast enhancement as seen on magnetic resonance imaging. These effects on the tumor vasculature may be mistakenly referred to as tumor responses because the historical method of measuring tumor response is based on tumor size assessed by contrast enhancement. This may explain why the few prospective phase II trials and several retrospective studies of Avastin in GBM report high radiographic response rates (30-60%) but modest improvements in progression-free survival and overall survival. Improved radiographic criteria for detecting disease progression in this context are needed and should be used in larger, randomized clinical trials which determine the magnitude of the survival benefit from Avastin.