Early change in glucose metabolic rate measured using FDG-PET in patients with high-grade glioma predicts response to temozolomide but not temozolomide plus radiotherapy.

Abstract

To compare the ability of positron emission tomography (PET) to predict response to temozolomide vs. temozolomide plus radiotherapy. Nineteen patients with high-grade glioma (HGG) were studied. Patients with recurrent glioma received temozolomide 75 mg/m2 daily for 7 weeks (n=8). Newly diagnosed patients received temozolomide 75 mg/m2 daily plus radiotherapy 60 Gy/30 fractions over 6 weeks, followed by six cycles of adjuvant temozolomide 200 mg/m2/day (Days 1-5 q28) starting 1 month after radiotherapy (n=11). [18F]Fluorodeoxyglucose ([18F]FDG) PET scan and magnetic resonance imaging (MRI) were performed at baseline, and 7 and 19 weeks after initiation of temozolomide administration. Changes in glucose metabolic rate (MRGlu) and MRI response were correlated with patient survival. In the temozolomide-alone group, patients who survived>26 vs. <or=26 weeks showed a greater reduction in MRGlu measured at 7 weeks with median changes of -34% and -4%, respectively (p=0.02). PET responders, defined as a reduction in MRGlu>or=25%, survived longer than nonresponders with mean survival times of 75 weeks (95% CI, 34-115 vs. 20 weeks (95% CI, 14-26) (p=0.0067). In the small group of patients studied, there was no relationship between MRI response and survival (p=0.52). For patients receiving temozolomide plus radiotherapy, there was no difference in survival between PET responders and nonresponders (p=0.32). Early changes in MRGlu predict response to temozolomide, but not temozolomide plus radiotherapy.