title: Combined analysis of O6-methylguanine-DNA methyltransferase protein expression and promoter methylation provides optimized prognostication of glioblastoma outcome.
abstract: BACKGROUND
  Promoter methylation of the DNA repair gene, O-6-methylguanine-DNA methyltransferase (MGMT), is associated with improved treatment outcome for newly diagnosed glioblastoma (GBM) treated with standard chemoradiation. To determine the prognostic significance of MGMT protein expression as assessed by immunohistochemistry (IHC) and its relationship with methylation, we analyzed MGMT expression and promoter methylation with survival in a retrospective patient cohort.
  
  
  METHODS
  We identified 418 patients with newly diagnosed GBM at University of California Los Angeles Kaiser Permanente Los Angeles, nearly all of whom received chemoradiation, and determined MGMT expression by IHC, and MGMT promoter methylation by methylation-specific PCR (MSP) and bisulfite sequencing (BiSEQ) of 24 neighboring CpG sites.
  
  
  RESULTS
  With use of the median percentage of cells staining by IHC as the threshold, patients with <30% staining had progression-free survival (PFS) of 10.9 months and overall survival (OS) of 20.5 months, compared with PFS of 7.8 months (P < .0001) and OS of 16.7 months (P < .0001) among patients with ≥30% staining. Inter- and intrareader correlation of IHC staining was high. Promoter methylation status by MSP was correlated with IHC staining. However, low IHC staining was frequently observed in the absence of promoter methylation. Increased methylation density determined by BiSEQ correlated with both decreased IHC staining and increased survival, providing a practical semiquantitative alternative to MSP. On the basis of multivariate analysis validated by bootstrap analysis, patients with tandem promoter methylation and low expression demonstrated improved OS and PFS, compared with the other combinations.
  
  
  CONCLUSIONS
  Optimal assessment of MGMT status as a prognostic biomarker for patients with newly diagnosed GBM treated with chemoradiation requires determination of both promoter methylation and IHC protein expression.
authors: Department of Neurology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California, USA.
authors: Shadi
authors: S
authors: Lalezari
authors: Arthur P
authors: AP
authors: Chou
authors: Anh
authors: A
authors: Tran
authors: Orestes E
authors: OE
authors: Solis
authors: Negar
authors: N
authors: Khanlou
authors: Weidong
authors: W
authors: Chen
authors: Sichen
authors: S
authors: Li
authors: Jose A
authors: JA
authors: Carrillo
authors: Reshmi
authors: R
authors: Chowdhury
authors: Julia
authors: J
authors: Selfridge
authors: Desiree E
authors: DE
authors: Sanchez
authors: Ryan W
authors: RW
authors: Wilson
authors: Mira
authors: M
authors: Zurayk
authors: Jonathan
authors: J
authors: Lalezari
authors: Jerry J
authors: JJ
authors: Lou
authors: Laurel
authors: L
authors: Ormiston
authors: Karen
authors: K
authors: Ancheta
authors: Robert
authors: R
authors: Hanna
authors: Paul
authors: P
authors: Miller
authors: David
authors: D
authors: Piccioni
authors: Benjamin M
authors: BM
authors: Ellingson
authors: Colin
authors: C
authors: Buchanan
authors: Paul S
authors: PS
authors: Mischel
authors: Phioanh L
authors: PL
authors: Nghiemphu
authors: Richard
authors: R
authors: Green
authors: He-Jing
authors: HJ
authors: Wang
authors: Whitney B
authors: WB
authors: Pope
authors: Linda M
authors: LM
authors: Liau
authors: Robert M
authors: RM
authors: Elashoff
authors: Timothy F
authors: TF
authors: Cloughesy
authors: William H
authors: WH
authors: Yong
authors: Albert
authors: A
authors: Lai
mesh_terms: D000328:Adult; D018906:Antineoplastic Agents, Alkylating / Q000627:therapeutic use; D001932:Brain Neoplasms / Q000235:genetics / Q000401:mortality* / Q000628:therapy; D059248:Chemoradiotherapy; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000235:genetics* / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000235:genetics* / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000235:genetics; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000627:therapeutic use; D005260:Female; D005500:Follow-Up Studies; D005909:Glioblastoma / Q000235:genetics / Q000401:mortality* / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D016133:Polymerase Chain Reaction; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012189:Retrospective Studies; D015996:Survival Rate; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018906:Antineoplastic Agents, Alkylating; D004273:DNA, Neoplasm; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes; D000077204:Temozolomide