The role of MGMT promotor hypermethylation as a predictive factor for response to temozolomide in recurrent high-grade glioma

Abstract

12509 Background: Epigenetic silencing of the MGMT (O6-methylguanine-DNA methyltransferase) DNA-repair gene by promotor hypermethylation (MGMT-meth) compromises DNA repair of high-grade glioma (HGG) and has been associated with a survival benefit in patients treated with temozolomide (TMZ) for newly diagnosed glioblastoma multiforme (GBM). It remains undetermined if the MGMT-meth status correlates with response to temozolomide at recurrence and whether extended dosing of TMZ (known to deplete MGMT in peripheral blood mononuclear cells) can overcome resistance in unmethylated HGG. Methods: We are investigating the MGMT-meth status on glioma tissue samples collected at diagnosis from 64 patients (pts). Fifty pts were treated at the time of recurrence with conventional TMZ (5 out of 28d regimen) and 14 pts with extended dosing of TMZ (100 mg/m2/d, 21 out of 28d regimen). Following DNA isolation from archival glioma tissues by phenol/chloroform extraction and a bisulphite conversion of genomic DNA, real-time methylation-specific PCR quantification of the methylation status of the MGMT promotor region is performed by OncoMethylome Sciences S.A. (according to OMS proprietary methodology). Results: At present, results have been obtained for 15 pts (13 M/ 2 W, median age: 46y). From 3 pts a biopsy at recurrence was available for analysis. The result was discordant with the MGMT-meth status at diagnosis in 2 pts (1x meth to unmeth and 1x unmeth to meth). Of the 6 (40%) pts with MGMT-meth gliomas, none had immediate progression on TMZ (respectively 4x SD, 1x CR, 1x PR). Of the 9 pts with an unmethylated MGMT promotor, 4 pts had immediate progression on TMZ and 5 pts had SD (of which 4 had been treated with the 21/28d regimen). All pts, except one, with MGMT-meth had a TTP that was above the median of our study population. The two pts with an MGMT-unmeth status that had a TTP above the median had received the extended dosing regimen. Conclusions: Our preliminary data indicate that MGMT promotor hypermethylation at diagnosis might correlate with sensitivity to TMZ in the recurrent setting. Extended dosing of TMZ might be more active against MGMT-unmethylated glioma. Final data from this study will be available for presentation at the meeting. No significant financial relationships to disclose.