CT-based response assessment of advanced gastrointestinal stromal tumor: dual energy CT provides a more predictive imaging biomarker of clinical benefit than RECIST or Choi criteria.

OBJECTIVES: Dual-energy CT (DECT) allows quantification of intravenously injected iodinated contrast media in tumors, and therefore may be considered as a surrogate marker for perfusion and tumor vascularity. This study evaluated whether newly developed DECT response criteria allow better correlation with survival than established response criteria.
METHODS: Seventeen patients with advanced GIST treated with tyrosine-kinase-inhibitors were assessed by contrast-enhanced DECT 2 and 6 months after beginning of treatment. Response to treatment of 165 tumor lesions was evaluated according to RECIST, Choi criteria and newly developed DECT criteria, defining non-responders as an increase of both tumor size >20% and iodine related attenuation or either a >50% increase of tumor size or iodine related attenuation. All other patients were classified as responders. Progression-free survival (PFS) and overall survival (OS) were calculated by Kaplan-Meier analysis.
RESULTS: Choi criteria and DECT showed a significantly longer median PFS of patients rated as responders than patients rated as non-responders (9-29 months vs. 2-6 months; p<0.02) at follow-up. Only DECT analysis at 6 months follow-up allowed a valid prediction of OS.
CONCLUSION: This study indicates that DECT allows a better prediction of therapeutic benefit in advanced GIST patients treated with tyrosine-kinase-inhibitors than established response criteria. However, the most important predictive biomarker of therapeutic benefit was absence of progression, no matter which response evaluation criteria were applied.