title: Low-level microsatellite instability phenotype in sporadic glioblastoma multiforme.
abstract: OBJECTIVE
  Genetic instability is a hallmark of glioblastoma multiforme (GBM). Microsatellite instability (MSI) is a significant event in the tumorigenesis of many sporadic malignancies. The aim of our investigation was to study microsatellite instability in newly diagnosed glioblastomas.
  
  
  METHODS
  MSI was investigated in 109 GBMs with 15 microsatellite markers. Immunohistochemistry was performed for the mismatch repair (MMR) proteins hMLH1, hMSH2, hPMS2, and hMSH6 in cases showing MSI. Sequence and promoter methylation status of hMLH1 were analyzed in the case of a decreased hMLH1 protein expression as well. To further investigate MSI(+) GBMs we carried out studies of LOH at selected chromosome regions, EGFR amplification, and sequence of p53 and PTEN.
  
  
  RESULTS
  MSI was observed in six GBMs (5.5%) and it was more frequent in GBMs with a previous lower grade astrocytoma (18.8% vs. 3.2%). MMR protein staining was positive in all MSI(+) GBMs except in one case, which showed an aberrant expression of hMLH1 and hPMS2 without hMLH1 inactivation. Among MSI(+) GBMs, one tumor corresponded to the GBM molecular type 1 (p53 mutation, no EGFR amplification), another tumor to type 2 (wild-type p53, EGFR amplification), and four tumors to neither type (wild-type p53, no EGFR amplification). None of the six tumors carried a PTEN mutation.
  
  
  CONCLUSIONS
  MSI in GBM might be caused by inactivation of minor MMR genes rather than by a deficiency of hMLH1 or hMSH2 and it appears not to play a decisive role in the pathogenesis of these tumors. MSI(+) GBMs predominantly showed a profile which included wild-type of p53 and PTEN and absence of EGFR amplification but MSI occurred in all GBM molecular subtypes.
authors.affiliation: Department of Neurosurgery, Klinikum Fulda, Academic Hospital University of Marburg, Pacelliallee 4, 36043 Fulda, Germany. voelter.martinez@t-online.de
authors.forename: R
authors.initials: R
authors.lastname: Martinez
authors.forename: H K
authors.initials: HK
authors.lastname: Schackert
authors.forename: H
authors.initials: H
authors.lastname: Appelt
authors.forename: J
authors.initials: J
authors.lastname: Plaschke
authors.forename: G
authors.initials: G
authors.lastname: Baretton
authors.forename: G
authors.initials: G
authors.lastname: Schackert
mesh_terms: D000293:Adolescent; D000328:Adult; D020137:Base Pair Mismatch / Q000235:genetics*; D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology*; D002471:Cell Transformation, Neoplastic; D004249:DNA Damage; D004260:DNA Repair; D005260:Female; D005909:Glioblastoma / Q000235:genetics* / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D010641:Phenotype