Abstract

BACKGROUND
The aim of this study was to determine whether pyrosequencing (PSQ) might be useful to achieve O6-methyl guanine methyltransferase (MGMT) promoter methylation using 1- to 13-year-old archival tissues as a clinical biomarker in routine practice.
METHODS
The study included 141 formalin-fixed paraffin-embedded (FFPE) glial tumors from the archives of the Pathology Department from 1997-2010.
RESULTS
The average percentage of methylation (MP) of the 141 cases was 14.0+/-16.8%, and methylated cases were 32.3+/-14.9%. The average MP of each year did not show a linear increasing or decreasing pattern according to the age of the FFPE block (p=0.771). The average MP of methylated glioblastomas was 35.8+/-14.7%, 31.8+/-15.5% for anaplastic astrocytomas, and 22.4+/-15.1% for astrocytoma. A tendency was observed toward an increasing pattern of average MP with World Health Organization (WHO) grade (p=0.063) in astrocytic tumors. A correlation was observed between average MP and WHO grade (p=0.038) and a bimodal distribution was observed between the methylated and unmethylated cases, using a 9% cut-off value (p<0.001).
CONCLUSIONS
The results showed that a quantitative approach for MGMT promoter methylation yielded a 100% success rate for FFPE tissues from archives. PSQ can be used in a retrospective trial, but the cut-off value and calculation method should be further validated.

• Keywords: Glioma;MGMT;Pyrosequencing;Biomarker;Methylation;