Objective: Several studies have demonstrated the effective use of adjuvant treatment with Imatinib mesylate for unresectable, metastatic or recurrent gastrointestinal stromal tumours (GIST). We retrospectively evaluated the role of 18F-FDG PET/CT scanning in assessing the response of GIST patients to imatinib mesylate therapy.
Materials and methods: Eight consecutive patients with GIST confirmed by surgery (4 stomach, 2 small bowel, 1 small bowel and peritoneum, and 1 rectum) underwent eighteen 18F-FDG PET/CT imaging after beginning imatinib mesylate therapy (400 mg/day or greater if disease progression). PET/CT scan was acquired 60-90 minutes after the intravenous injection of 333-707 MBq of 18F-FDG. Visual and semiquantitative (standardized uptake value [SUV]) analysis of images was performed. Response to therapy was assessed according to EORTC recommendations for PET. Results were confirmed by clinical follow-up, radiographic findings or histological analysis.
Results: Complete response to imatinib mesylate was observed in 5 patients. Four had abdominal lymph nodes, associated with liver metastases in 2, and the other had a residual tumour mass. Partial response (reduction in SUV and in the extent of FDG uptake) was demonstrated in a patient with lung nodules. Disease progression was observed in one patient who had developed new liver metastases on the PET/CT scan. One patient with multiple peritoneal implants and abdominal mass was a non-responder and died 2 months after the 18F-FDG PET/CT.
Conclusion: 18F-FDG PET/CT scan identified the degree of GIST response to imatinib therapy. Patients who responded to therapy showed normalisation of FDG uptake or a decrease in the SUV of lesions.