Impact on prognosis of the regional distribution of MGMT methylation with respect to the CpG island methylator phenotype and age in glioma patients

• Published in: Journal of neuro-oncology Vol. 122; no. 3; pp. 441 - 450
• Main Authors: Mur, Pilar, Rodríguez de Lope, Ángel, Díaz-Crespo, Francisco Javier, Hernández-Iglesias, Teresa, Ribalta, Teresa, Fiaño, Concepción, García, Juan Fernando, Rey, Juan Antonio, Mollejo, Manuela, Meléndez, Bárbara
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-05-2015; Springer Nature B.V
• Subjects: Adult; Age Factors; Aged; Brain Neoplasms - diagnosis; Brain Neoplasms - genetics; Brain Neoplasms - mortality; CpG Islands - genetics; DNA Methylation - genetics; DNA Modification Methylases - genetics; DNA Repair Enzymes - genetics; Female; Gene Expression Profiling; Glioma - diagnosis; Glioma - genetics; Glioma - mortality; Humans; Laboratory Investigation; Male; Medicine; Medicine & Public Health; Middle Aged; Neurology; Oligonucleotide Array Sequence Analysis; Oncology; Phenotype; Principal Component Analysis; Prognosis; Promoter Regions, Genetic - genetics; Survival Analysis; Tumor Suppressor Proteins - genetics; Young Adult; mutation; CpG island methylator phenotype; Glioma; Overall survival; methylation
• ISSN: 0167-594X; 1573-7373
• DOI: 10.1007/s11060-015-1738-9

Clinical and molecular prognostic factors in gliomas include age,
IDH
mutation, the glioma CpG island methylator phenotype (G-CIMP+) and promoter methylation of the O
6
-methylguanine DNA-methyltransferase (
MGMT
) gene. Among these markers, a predictive value was reported in glioblastomas (GBM) for
MGMT
promoter methylation, in particular in elderly GBM patients. In this study, methylation data from 46 glioma samples with the Illumina 450K platform were obtained and extended using external data to include a total of 247 glioma samples. Methylation analysis of the whole
MGMT
gene with this platform revealed two strongly survival-associated CpG regions within the promoter and the gene body, which were confirmed in a reported dataset of high grade-gliomas. Methylation at the promoter (CpG 25, cg12981137 and the prognostic model
MGMT
-STP27) and at the gene body CpG 165 (cg07933035), were significantly associated with better overall survival, and strongly correlated with G-CIMP+ status. In this series, the prognostic value of
MGMT
methylation at the promoter was not observed in G-CIMP− cases, although around 50 % of them were
MGMT
-methylated. These results were also obtained in an homogeneously-treated series of chemoradiated G-CIMP− GBMs analyzed by MSP and qMSP, and confirmed in a reported pyrosequencing-analyzed series of gliomas. Interestingly, in contrast to the
MGMT
promoter, gene body methylation was of prognostic value in G-CIMP−patients older than 65 years. Our study highlights the relevance of the prognostic value of the different regions of methylation throughout the
MGMT
gene that could be affected by specific G-CIMP profiles and age groups.