• D Fuster, J R Ayuso, A Poveda, R Cubedo, A Casado, J Martínez-Trufero, A López-Pousa, X G Del Muro, F Lomeña, J Maurel, and F Pons.
• Nuclear Medicine, Hospital Clínic Barcelona, Barcelona, Spain. dfuster@clinic.ub.es
• Q J Nucl Med Mol Imaging. 2011 Dec 1; 55 (6): 680-7.

AimThe aim of this study was to evaluate the utility of positron emission tomography with 18F-fluorodeoxyglucose (FDG-PET) in monitoring response in refractory GIST.MethodsThis multicenter study prospectively evaluated 21 patients with locally advanced and/or metastatic GIST refractory to with high-dose imatinib (800 mg/day) treated with doxorubicin 15-20 mg/m2/weekly for 4 cycles, followed by imatinib maintenance (400 mg/day). CT and FDG-PET were performed at baseline and after completion of therapy.ResultsMean baseline tumor size on CT was 5.9 cm. Median progression-free survival (PFS) was 219 days (range 62-1108). Three out of 21 patients (14%) had partial responses (PR) under RECIST criteria, 12 patients (57%) remained stable (SD) and 6 showed progression (PD) of the disease during treatment (29%). Six patients had PR by FDG-PET, 15 showed SD (n=9) or PD (n=6) based on EORTC criteria. Patients with a PFS <6 mo showed a significantly higher ∑SUVmax at baseline (26.04±13.4) than those with PFS≥6 mo (9.82±5.0) (P<0.05). A correlation was found between PET response and PFS: PR 14±6.1 mo, SD 5.5±0.8 mo and PD 3.5±4.1 mo (P<0.05). A residual SUVmax <5 after treatment correlated with improved PFS (314±315 days vs 131±91 days) (P<0.01). Survival curves showed a significant association between PET response and PFS (P<0.05). Patients with wild-type genotype KIT (KIT-WT) showed a significantly lower baseline SUVmax (5.36±1.4) than non-WT KIT (8.40±3.6) (P<0.05).ConclusionFDG-PET is useful in assessing response of GIST refractory to imatinib and correlates with the presence of KIT-WT. Baseline ∑SUVmax can predict response to treatment in this series.

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