MGMT promoter methylation in gliomas-assessment by pyrosequencing and quantitative methylation-specific PCR

Background: Methylation of the O-6-methylguanine-DNA methyltransferase (MGMT) gene promoter is a favorable prognostic factor in glioblastoma patients. However, reported methylation frequencies vary significantly partly due to lack of consensus in the choice of analytical method. Method: We examined 35 low-and 99 high-grade gliomas using quantitative methylation specific PCR (qMSP) and pyrosequencing. Gene expression level of MGMT was analyzed by RT-PCR. Results: When examined by qMSP, 26% of low-grade and 37% of high-grade gliomas were found to be methylated, whereas 97% of low-grade and 55% of high-grade gliomas were found methylated by pyrosequencing. The average MGMT gene expression level was significantly lower in the group of patients with a methylated promoter independent of method used for methylation detection. Primary glioblastoma patients with a methylated MGMT promoter (as evaluated by both methylation detection methods) had approximately 5 months longer median survival compared to patients with an unmethylated promoter (log-rank test; pyrosequencing P = .02, qMSP P = .06). One third of the analyzed samples had conflicting methylation results when comparing the data from the qMSP and pyrosequencing. The overall survival analysis shows that these patients have an intermediate prognosis between the groups with concordant MGMT promoter methylation results when comparing the two methods. Conclusion: In our opinion, MGMT promoter methylation analysis gives sufficient prognostic information to merit its inclusion in the standard management of patients with high-grade gliomas, and in this study pyrosequencing came across as the better analytical method.