title: The prognostic significance of whole blood global and specific DNA methylation levels in gastric adenocarcinoma.
abstract: BACKGROUND
  Epigenetics, particularly DNA methylation, has recently been elucidated as important in gastric cancer (GC) initiation and progression. We investigated the clinical and prognostic importance of whole blood global and site-specific DNA methylation in GC.
  
  
  METHODS
  Genomic DNA was extracted from the peripheral blood of 105 Omani GC patients at diagnosis. DNA methylation was quantified by pyrosequencing of global DNA and specific gene promoter regions at 5 CpG sites for CDH1, 7 CpG sites for p16, 4 CpG sites for p53, and 3 CpG sites for RUNX3. DNA methylation levels in patients were categorized into low, medium, and high tertiles. Associations between methylation level category and clinicopathological features were evaluated using χ(2) tests. Survival analyses were carried out using the Kaplan-Meier method and log rank test. A backward conditional Cox proportional hazards regression model was used to identify independent predictors of survival.
  
  
  RESULTS
  Older GC patients had increased methylation levels at specific CpG sites within the CDH1, p53, and RUNX-3 promoters. Male gender was significantly associated with reduced global and increased site-specific DNA methylation levels in CDH1, p16, and p53 promoters. Global DNA low methylation level was associated with better survival on univariate analysis. Patients with high and medium methylation vs. low methylation levels across p16 promoter CpG sites, site 2 in particular, had better survival. Multivariate analysis showed that global DNA hypermethylation was a significant independent predictor of worse survival (hazard ratio (HR) = 2.0, 95% CI: 1.1-3.8; p = 0.02) and high methylation mean values across p16 promoter sites 1-7 were associated with better survival with HR of 0.3 (95% CI, 0.1-0.8; p = 0.02) respectively.
  
  
  CONCLUSIONS
  Analysis of global and site-specific DNA methylation in peripheral blood by pyrosequencing provides quantitative DNA methylation values that may serve as important prognostic indicators.
authors.affiliation: Medical Oncology Unit, Department of Medicine, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman. mansours@squ.edu.om
authors.forename: Mansour S
authors.initials: MS
authors.lastname: Al-Moundhri
authors.forename: Maryam
authors.initials: M
authors.lastname: Al-Nabhani
authors.forename: Letizia
authors.initials: L
authors.lastname: Tarantini
authors.forename: Andrea
authors.initials: A
authors.lastname: Baccarelli
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Rusiecki
mesh_terms: D000230:Adenocarcinoma / Q000097:blood / Q000235:genetics*; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins / Q000235:genetics; D050677:Core Binding Factor Alpha 3 Subunit / Q000235:genetics; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D019175:DNA Methylation; D018450:Disease Progression; D044127:Epigenesis, Genetic; D006801:Humans; D011379:Prognosis; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D013274:Stomach Neoplasms / Q000097:blood / Q000235:genetics*; D013447:Sulfites / Q000737:chemistry; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D050677:Core Binding Factor Alpha 3 Subunit; D019941:Cyclin-Dependent Kinase Inhibitor p16; C577585:Fzr1 protein, mouse; D013447:Sulfites; D016159:Tumor Suppressor Protein p53; D004247:DNA; C042345:hydrogen sulfite