Effect of angio-echography with a second-generation contrast agent to assess tumor response to imatinib treatment in patients with advanced gastrointestinal stromal tumor (GIST): Comparison with computerized tomography (CT)

Abstract

4216 Background: GIST metastases are typically intra-abdominal and hypervascular. BR1 (Sonovue, Bracco, Milan, Italy) is a new blood pool second-generation contrast agent, which consists of stabilized microbubbles of a totally innocuous sulphur hexafluoride gas. We report preliminary results with angio-echography with BR1 (AE) to assess tumor response (TR) to imatinib treatment (IT) in patients (pts) with advanced GIST. Methods: Twelve consecutive pts with known advanced cKIT+ GIST were investigated prospectively. CT and AE were performed before IT and then at 1, 2, 4, 6, and then every 3 months during IT. A strict prospective evaluation with AE was performed in 2 pts at 1, 2, 4, 6, 8 weeks during IT. Results: At a median follow-up of 12 months (range 4–18), in the 11 evaluable pts CT documented TR in 5 (46%) pts and stable disease (SD) in 4 (36%) RECIST criteria), while AE showed early TR in all these 9 (82%) cases. The median time to TR by RECIST criteria at CT was 4 months (range 1–9), while TR was observed at the first AE, and after 2 weeks in the 2 cases receiving strict AE evaluation. During IT, in 1 case CT showed increase of liver metastases, but AE demonstrated TR with intra-tumoral edema. Compared with CT, AE better depicted liver subcentimetric metastases. No differences between CT and AE were seen in the evaluation of extra-hepatic metastases. Conclusions: In large studies, CT (RECIST criteria) showed TR (54%) or SD (34%) associated with IT, which correlated closely with a finding of ≥50% decrease in FDG uptake on PET scan in 89% of pts. In our study, AE improved the display of tumor vascularity as well as the accuracy in differentiating between SD and TR. The effective TR to IT in GISTs might be superior to that showed by CT only, according to RECIST criteria. The close relation between clinical outcome and the findings on AE indicates that such scanning might be an useful complement to standard anatomical imaging for monitoring the therapeutic effect of imatinib in pts with GIST. Large prospective studies are warranted. No significant financial relationships to disclose.