Abstract 2707: Impact of accuracy in O6-methylguanine-DNA methyltransferase methylation assays for temozolomide efficacy on glioblastoma

Abstract Background: O6-methylguanine-DNA methyltransferase (MGMT) is implicated in resistance to temozolomide (TMZ). MGMT status has been shown to correlate with survival of patients with glioblastoma (GBM). We evaluated the relationship between promoter methylation status and protein expression of the MGMT gene in patients with GBM treated with TMZ, and also analyzed their prognostic value regarding response to TMZ and survival. Methods: We analyzed 47 GBM tissues from 43 patients treated with TMZ from September 2003 to January 2009. Among them, 22 patients with recurrent GBM treated with standard TMZ single therapy were subjected to survival analyses. TMZ was given daily orally 75mg/m2 during radiotherapy, or as standard 5/28-day regimen. MGMT protein expression was quantified by Western blotting, and promoter methylation status was determined by both methylation-specific PCR (MSP) and quantitative pyrosequencing. Results: MGMT promoter methylation was detected in 19/47 cases (40.4%) by MSP, 16/47 (34%) by pyrosequencing, and was significantly correlated with each other (p<0.001). The methylation status correlated significantly with MGMT protein expression as well. Upon TMZ treatment for recurrent GBM, patients with both methylated MGMT promoter by MSP and low MGMT protein expression had a significantly improved progression-free survival (PFS) and overall survival (OS), whereas methylation status by pyrosequencing data did not. MGMT status was the only significant prognostic factor for PFS and OS. Conclusions: The three MGMT assays revealed similar methylation/expression patterns and were suggested to be important prognostic factors for patients treated with TMZ. Whether precise quantification of the methylation status provides any clinically relevant information on the treatment strategy for GBM needs to be further investigated. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2707.