Very early detection of response to imatinib mesylate therapy of gastrointestinal stromal tumours using 18fluoro-deoxyglucose-positron emission tomography.

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.