Abstract:
Background: Genome-wide hypomethylation is one of the cancer characteristics. In glioblastoma multiforme (GBM), hypermethylation of MGMT promoter serves as an important prognostic and a predictive factor for response to alkylating agents. Recent evidence demonstrates that level of genome-wide methylation assessed by measuring level of LINE-1 methylation in glioblastomas is lower compared with those of low-grade gliomas. Objective: To determine the correlation between the localized methylation in the MGMT promoter and the global DNA methylation in glioblastomas. Methods: We collected 70 formalin-fixed, paraffin-embedded GBM tissues derived from patients treated at the King Chulalongkorn Memorial Hospital during year 2008-2013. To define MGMT promoter methylation status, we used pyrosequencing and methylation specific polymerase chain reaction (MSP) technique. And pyrosequencing was used to determine the percentage of methylation of LINE-1. Results: There were 70 GBMs included in this study. The median level of LINE-1 and MGMT promoter methylation were 66.6% and 8.2%, respectively. High LINE-1 methylation (>68%) was found in 41% of the patients. MGMT promoter hypermethylation was described in 30% and 25.7% by MSP and pyrosequencing (>22.7%), respectively. There were 9 patients with discordant MGMT promoter methylation status between these two techniques. There was no correlation between LINE-1 methylation and MGMT promoter methylation (r=0.094, p=0.44). Conclusion: In limit number of glioblastomas, there is no correlation between genome-wide methylation and MGMT promoter methylation status. Low LINE-1 methylation was associated with a trend for better survival. Further studies in larger population are warranted.