The Clinical Implications of Inconsistently Methylated Results from Glioblastoma MGMT Testing by Replicate Methylation Specific PCR.
The methylation status of the promoter of the O6 methylguanine DNA methyltransferase gene (MGMT) is an established prognostic and predictive biomarker of glioblastoma (GBM) At the Center for Advanced Molecular Diagnostics, MGMT testing is performed by methylation specific PCR with multiple replicates, leading to three types of reportable results: methylated, unmethylated, and inconsistently methylated. An inconsistently methylated result is reported when a methylated peak is seen in some but not all of the PCR replicates from a single DNA sample. To better understand the clinical implications of these results, we performed a retrospective review of all MGMT testing at our laboratory over a 5 year period, and correlated test results with outcome and specimen quality data. This review yielded several novel findings. First, inconsistent MGMT methylation on replicate methylation specific PCR is not uncommon, composes 12% (58/465) of our GBM results. Second, inconsistently methylated GBM cases are associated with relatively poor overall survival (more similar to unmethylated than to methylated cases) Third and interestingly, there appears to be a dose response relationship between patient survival and the extent of methylation in inconsistently methylated GBMs. Finally, our analyses of specimen quality data suggest that a combination of technical factors (eg, small samples) and tumor biology may explain inconsistent MGMT results on replicate methylation specific PCR testing.
The Journal of molecular diagnostics JMD