PATH-01. MGMT METHYLATION CUTOFF VALUE IN QUANTITATIVE ANALYSIS RELATED TO PROGNOSIS OF NEWLY DIAGNOSED GLIOBLASTOMA

Abstract

Abstract BACKGROUND MGMT promoter methylation is an important biomarker related to glioblastoma therapeutic response and prognosis. There are qualitative and quantitative methods as assays for MGMT methylation. Although the qualitative method is common, there is a disadvantage that low or high methylation cannot be distinguished. The quantitative method is an excellent method for evaluating methylation of tumors characterized by intratumoral heterogeneity like malignant glioma, but cutoff value of methylation that defines the prognosis of glioblastoma is unknown. Therefore, we examined the cutoff value of quantitative MGMT methylation assay determining the prognosis in glioblastoma. METHODS 180 newly diagnosed glioblastoma which underwent radiotherapy and temozolomide treatment after tumor removal in our department were included. MGMT methylation was quantitatively analyzed by methylation-specific high resolution melting (MS-HRM) analysis. For each level of methylation, progression-free survival (PFS) and overall survival (OS) were calculated and statistically analyzed. RESULTS In the low MGMT methylation cases in which the proportion of methylation was 25% or less in PFS and 30% or less in OS, no difference was observed in PFS and OS as compared with those of unmethylated cases. The cutoff value of MGMT methylation most contributing to survival was calculated to be 35% by the survival classification and regression tree method. CONCLUSION The prognosis for MGMT hypomethylated group is as poor as unmethylated one. In the quantitative MS-HRM method, we found that the value of MGMT methylation of 35% is useful as a cut off determining the prognosis of glioblastoma.