Quantitative functional imaging by Dynamic Contrast Enhanced Ultrasonography (DCE-US) in GIST patients treated with masatinib

Objectives: To determine the quantitative parameters of DCE-US for predicting early functional response of patients with metastatic gastrointestinal stromal tumors (GIST). Materials and methods: Phase II multicentre clinical trial in patients with metastatic GIST treated with masatinib mesylate (7.5 mg/kg daily by oral route) Patients followed using three different imaging techniques: 1) DCE-US before treatment and on days 1, 7, 15 and after 1, 2, 4, 6 months and every 3 months. 2) CT assessments, using RECIST criteria, before treatment, after 2, 4, 6 months and then every 3 months. 3) FDG PET before treatment and after 1 month. Results: Twenty patients included and followed-up for up to 36 months, with 269 DCE-US examinations performed. No significant changes in the 7 selected DCE-US variables on day 1 and 7 vs baseline. On day 15, significant reductions in all the variables related to blood volume recorded: area under the curve (AUC) (p=0. 004), area under the wash-in (AUWI) (p=0.002), area under the wash-out (AUWO) (p=0.002) and Peak Intensity (p=0.005). Also slope of wash-in changed significantly (p=0.003). An important reduction in Standard Uptake Values (SUV) recorded in 7/11 patients (PFS >18 months). Decrease in DCE-US AUC, AUWI and AUWO values on day 7 were predictive of PET-CT results. Conclusions: AUC AUWI, AUWO are the DCE-US parameters related to blood volume that at D 15 can predict the response of GISTs to treatment with masatinib. Additional studies are ongoing.