Prognostic Relevance of Tumor Purity and Interaction with MGMT Methylation in Glioblastoma.
Promoter methylation status of O-6-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme, is a critical biomarker in glioblastoma (GBM), as treatment decisions and clinical trial inclusion rely on its accurate assessment. However, interpretation of results is complicated by poor interassay reproducibility as well as a weak correlation between methylation status and expression levels of MGMT. This study systematically investigates the influence of tumor purity on tissue subjected to MGMT analysis. A quantitative, allele-specific real-time PCR (qAS-PCR) assay was developed to determine genotype and mutant allele frequency of telomerase promoter (pTERT) mutations as a direct measure of tumor purity. We studied tumor purity, pTERT mutation by Sanger sequencing, MGMT methylation by pyrosequencing, IDH1 mutation status, and clinical parameters in a cohort of high-grade gliomas (n= 97). The qAS-PCR reliably predicted pTERT genotype and tumor purity compared with independent methods. Tumor purity positively and significantly correlated with the extent of methylation in MGMT methylated GBMs. Extent of MGMT methylation differed significantly with respect to pTERT mutation hotspot (C228T vs. C250T). Interestingly, frontal lobe tumors showed greater tumor purity than those in other locations. Above all, tumor purity was identified as an independent prognostic factor in GBM. In conclusion, we determined mutual associations of tumor purity with MGMT methylation and pTERT mutations and found that the extent of MGMT methylation reflects tumor purity. In turn, tumor purity is prognostic in IDH1 wild-type GBM.Implications:Tumor purity is an independent prognostic marker in glioblastoma and is associated with the extent of MGMT methylation.Mol Cancer Res; 15(5); 532-40. ©2017 AACR.
Department of Experimental Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Eva
E
Schulze Heuling
Department of Experimental Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Felix
F
Knab
Department of Neuropathology, Charité - Universitätsmedizin Berlin, Berlin, Germany.|German Consortium for Translational Cancer Research (DKTK), Heidelberg, Germany.|Berlin Institute of Health (BIH), Berlin, Germany.
Josefine
J
Radke
Department of Genomic Medicine, University of Texas MD Anderson Cancer Center, Houston, Texas.
Eskil
E
Eskilsson
Department of Genomic Medicine, University of Texas MD Anderson Cancer Center, Houston, Texas.
Emmanuel
E
Martinez-Ledesma
Department of Neuropathology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Arend
A
Koch
Department of Neurosurgery, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Marcus
M
Czabanka
Computational RNA Biology and Ageing Group, Max-Planck-Institute for the Biology of Ageing, Cologne, Germany.
Christoph
C
Dieterich
Department of Genomic Medicine, University of Texas MD Anderson Cancer Center, Houston, Texas.|Department of Bioinformatics and Computational Biology, University of Texas MD Anderson Cancer Center, Houston, Texas.
Roel G
RG
Verhaak
Department of Experimental Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany. philipp.euskirchen@charite.de christoph.harms@charite.de.|Berlin Institute of Health (BIH), Berlin, Germany.|Center for Stroke Research Berlin, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Christoph
C
Harms
Department of Experimental Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany. philipp.euskirchen@charite.de christoph.harms@charite.de.|Berlin Institute of Health (BIH), Berlin, Germany.|Department of Neurology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Philipp
P
Euskirchen
D001932:Brain Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000235:genetics*; D044127:Epigenesis, Genetic; D005838:Genotype; D005909:Glioblastoma / Q000235:genetics*; D006801:Humans; D009154:Mutation; D011379:Prognosis; D011401:Promoter Regions, Genetic; D060888:Real-Time Polymerase Chain Reaction; D015203:Reproducibility of Results; D017422:Sequence Analysis, DNA; D016019:Survival Analysis; D025521:Tumor Suppressor Proteins / Q000235:genetics*
D025521:Tumor Suppressor Proteins; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes