Objective: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract with 70% of all GISTs are found in the stomach. The management of gastrointestinal stromal tumors (GISTs) has been revolutionized with the introduction of Imatinib mysylate as a targeted therapeutic agent and the dramatic change in the tumor metabolic activity following successful therapy with follow up using (FDG)-PET/CT. Patients and Methods: 47 consecutive patients (mean age: 49.2±12.7) with histologically proven GIST underwent whole-body FDG-PET/CT. A clinical/radiological CT and PET/CT follow-up for 3-15 months duration served as standards of reference. Results: There was no difference between CT and PET/CT in the initial staging of GIST or in detection of primary /recurrent lesions. A higher PET CT value in assessment of target therapy response was found in 11 patients (28%) compared to CT. Regarding patients prognosis 66.7 % of patients with lymph nodes metastases showed disease progression. In addition, 92.3% of patients who had complete metabolic remission or stable disease on follow up PET CT and did not had any newly developed metastases, while 55.5 % of patients who died or progressed on follow up PET/CT had double/triple organ metastases (5 patients), with statistically significant difference (P <0.001). No statistically significant relation was found between prognosis and patient`s age, sex, site of primary GIST. Conclusion: Combined PET/CT can provide additional functional information as compared with diagnostic CT in GIST, especially in therapy assessment.
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