Objective. The usefulness of 18F-fluoro-2-deoxyglucose positron emission tomography (18FDG-PET), whose high rate of FDG accumulation indicates high metabolism and malignant potential, has already been reported. The aims of this study were to evaluate the malignancy of primary gastrointestinal stromal tumour (GIST) in the stomach by 18FDG-PET and to correlate the FDG uptake values with known risk factors as determined by histology after EUS-guided fine needle aspiration (EUS-FNA) or endoscopic biopsy. Material and Methods. Of 29 patients with histologically proven GI-mesenchymal tumours, 21 with gastric GISTs underwent 18FDG-PET. Tumour size, mitotic index, Ki-67 labelling index (LI) and cellularity of the tumour tissue were compared with the standardized uptake value (SUV) of FDG. Results. Strong correlations were found between the SUV of FDG and EUS size, and mitotic index of EUS-FNA specimens (tumour size versus SUV, p=0.004, r=0.542; number of mitotic cells versus SUV, p=0.0078; n=21). Moreover, we examined the association between SUV and risk categories based on EUS-FNA findings using ROC curves. The cut-off values of FDG SUV were 2.2, 4.2 and 6.5 for the very low-, low-, intermediate- and high-risk groups, respectively. Conclusions. 18FDG-PET may be used to assess malignancy of GISTs. This image modality helps us determine the management strategy for these patients and complements the information on the biological behaviour and cellular proliferation of the tumours.
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