title: The Clinical Implications of Inconsistently Methylated Results from Glioblastoma MGMT Testing by Replicate Methylation-Specific PCR.
abstract: 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.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts. Electronic address: yxia8@partners.org.
authors.forename: Daniel
authors.initials: D
authors.lastname: Xia
authors.affiliation: Center for Neuro-Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: David A
authors.initials: DA
authors.lastname: Reardon
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Jacqueline L
authors.initials: JL
authors.lastname: Bruce
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts.
authors.forename: Neal I
authors.initials: NI
authors.lastname: Lindeman
mesh_terms: D001932:Brain Neoplasms / Q000175:diagnosis* / Q000235:genetics*; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000235:genetics*; D005260:Female; D005909:Glioblastoma / Q000175:diagnosis* / Q000235:genetics* / Q000401:mortality; D006801:Humans; D008297:Male; D060787:Neoplasm Grading; D016133:Polymerase Chain Reaction / Q000379:methods; D011379:Prognosis; D011401:Promoter Regions, Genetic; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes