Very Early Detection of Response to Imatinib Mesylate Therapy of Gastrointestinal Stromal Tumours Using 18Fluoro-Deoxyglucose-Positron Emission Tomography

Abstract

Aim: To investigate whether ¹⁸F-FDG-PET allows early assessment of response to imatinib mesylate in GIST patients. Patients and Methods: Five gastrointestinal stromal tumour (GIST) patients and one patient with a KIT-positive small cell cancer were studied. Treatment consisted of 400 mg imatinib mesylate daily. ¹⁸F-deoxyglucose-positron emission tomography (¹⁸F-FDG-PET) scans were done before and one week after starting imatinib mesylate therapy. Results: Metabolic responses were detected after only one week of therapy in all GIST patients (four partial and one complete response). The mean decrease of the standardised uptake value was 60% (range 43 to 77%). In contrast, the tumour of the non-GIST patient was metabolically stable. Four of the 5 GIST patients achieved a partial response on CT after a mean duration of 23 weeks (range 6 to 48 weeks). Conclusion: ¹⁸F-FDG-PET is a valuable method for the detection of response to imatinib mesylate in patients with KIT-positive tumours as early as one week after starting therapy.