Abstract
1532 Background: Temozolomide plus radiotherapy should now be the standard of care for patients with HGG (Stupp et al 2004; J Clin Oncol 22, 14S:2). We have previously shown that PET measurements of MRGlu can predict temozolomide response (Brock et al 2000; Br J Cancer 82:608–615). In this study, we compared the ability of PET to predict response to temozolomide vs temozolomide plus radiotherapy. Methods: 19 patients with HGG were studied. Patients with recurrent glioma received temozolomide 75mg/m2 daily for 7 weeks (n=8). Newly diagnosed patients received temozolomide 75mg/m2 daily plus radiotherapy 60Gy/30# over 6 weeks, followed by 6 cycles of adjuvant temozolamide (n=11). FDG PET scan and MRI were performed at baseline, and 7 and 19 weeks following initiation of treatment. Changes in MRGlu and MRI response were correlated with patient survival. Results: In patients receiving temozolomide alone, we confirmed our previous finding that early changes in MRGlu predicted response. Patients who survived >26 weeks vs ≤26 weeks showed a greater reduction in MRGlu measured at 7 weeks with median reductions of -34% and -4%, respectively (p=0.02). PET responders, defined as a reduction in MRGlu ≥25% (EORTC Guidelines 1999 Eur J Ca 35:1773–1782), had a longer survival than non-responders with mean survival times of 75 wks [95% CI 34–115] vs 20 wks [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 radiotherapy, there was no difference in survival between PET responders and non-responders (p=0.32). However, when PET response was measured 19 weeks following the initiation of treatment, there was a trend for increased survival in PET responders compared with non-responders (n=11, p=0.16). Conclusions: Early changes in MRGlu predict response to temozolomide, but not temozolomide plus radiotherapy. This may be due to the infiltration of tumours by glycolytic inflammatory cells following radiotherapy. FDG-PET assessment of radiotherapy response should be made later than for chemotherapy. No significant financial relationships to disclose.
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