Identifying the optimal cutoff point for MGMT promoter methylation status in glioblastoma.

To define the optimal cutoff point for determining methylation status of O6-methylguanine-DNA methyltransferase (MGMT) by pyrosequencing in glioblastoma.  A retrospective study of 109 glioblastoma patients was performed to determine the optimal cutoff point for MGMT methylation status. Receiver operating characteristic (ROC) analysis revealed 21% as the optimal cutoff (sensitivity: 68%; specificity: 59%) for MGMT methylation corresponding with the highest likelihood ratio of 1.66 and accuracy of 0.65. Methylation status (hazard ratio: 0.453; 95% CI: 0.279-0.735; p = 0.001) was associated with better overall survival. The crude model indicated linearity between methylation percent and survival rate; an increase of 10% of methylation resulted in a reduction of risk of death by 20% (p = 0.004). ROC analysis determined 21% as the optimal cutoff point for MGMT methylation status by pyrosequencing.