title: MGMT promoter hypermethylation and its associations with genetic alterations in a series of 350 brain tumors.
abstract: MGMT (O⁶-methylguanine-DNA methyltransferase) promoter hypermethylation is a helpful prognostic marker for chemotherapy of gliomas, although with some controversy for low-grade tumors. The objective of this study was to retrospectively investigate MGMT promoter hypermethylation status for a series of 350 human brain tumors, including 275 gliomas of different malignancy grade, 21 glioblastoma multiforme (GBM) cell lines, and 75 non-glial tumors. The analysis was performed by methylation-specific PCR and capillary electrophoresis. MGMT expression at the protein level was also evaluated by both immunohistochemistry (IHC) and western blotting analysis. Associations of MGMT hypermethylation with IDH1/IDH2 mutations, EGFR amplification, TP53 mutations, and 1p/19q co-deletion, and the prognostic significance of these, were investigated for the gliomas. MGMT promoter hypermethylation was identified in 37.8% of gliomas, but was not present in non-glial tumors, with the exception of one primitive neuroectodermal tumor (PNET). The frequency was similar for all the astrocytic gliomas, with no correlation with histological grade. Significantly higher values were obtained for oligodendrogliomas. MGMT promoter hypermethylation was significantly associated with IDH1/IDH2 mutations (P = 0.0207) in grade II–III tumors, whereas it had a borderline association with 1p deletion (P = 0.0538) in oligodendrogliomas. No other association was found. Significant correlation of MGMT hypermethylation with MGMT protein expression was identified by IHC in GBMs and oligodendrogliomas (P = 0.0001), but not by western blotting. A positive correlation between MGMT protein expression, as detected by either IHC or western blotting, was also observed. The latter was consistent with MGMT promoter hypermethylation status in GBM cell lines. In low-grade gliomas, MGMT hypermethylation, but not MGMT protein expression, was associated with a trend, only, toward better survival, in contrast with GBMs, for which it had favorable prognostic significance.
authors.affiliation: Neuro-bio-oncology Center, Policlinico di Monza Foundation, Via Pietro Micca, 29–13100, Vercelli, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Mellai
authors.forename: Oriana
authors.initials: O
authors.lastname: Monzeglio
authors.forename: Angela
authors.initials: A
authors.lastname: Piazzi
authors.forename: Valentina
authors.initials: V
authors.lastname: Caldera
authors.forename: Laura
authors.initials: L
authors.lastname: Annovazzi
authors.forename: Paola
authors.initials: P
authors.lastname: Cassoni
authors.forename: Guido
authors.initials: G
authors.lastname: Valente
authors.forename: Susanna
authors.initials: S
authors.lastname: Cordera
authors.forename: Cristina
authors.initials: C
authors.lastname: Mocellini
authors.forename: Davide
authors.initials: D
authors.lastname: Schiffer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics*; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D019175:DNA Methylation / Q000235:genetics*; D015254:DNA Modification Methylases / Q000235:genetics*; D004252:DNA Mutational Analysis; D045643:DNA Repair Enzymes / Q000235:genetics*; D005260:Female; D005784:Gene Amplification; D018773:Genes, erbB-1 / Q000235:genetics; D016158:Genes, p53 / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D007521:Isocitrate Dehydrogenase / Q000235:genetics; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009154:Mutation; D060787:Neoplasm Grading; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012189:Retrospective Studies; D025521:Tumor Suppressor Proteins / Q000235:genetics*; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D025521:Tumor Suppressor Proteins; C538784:IDH2 protein, human; D007521:Isocitrate Dehydrogenase; C543588:IDH1 protein, human; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes