DNA methylation in peripheral blood and risk of gastric cancer: a prospective nested case-control study.

DNA methylation in peripheral blood is a potential biomarker of gastric cancer risk which could be used for early detection. We conducted a prospective case-control study nested within the Melbourne Collaborative Cohort Study. Genomic DNA was prepared from blood samples collected a median of 12 years before diagnosis for cases (N=168). Controls (N=163) were matched to cases on sex, year of birth, country of birth and blood sample type using incidence density sampling. Genome-wide DNA methylation was measured using the Infinium HumanMethylation450K Beadchip. Global measures of DNA methylation were defined as the median methylation M-value, calculated for each of 13 CpG subsets representing genomic function, mean methylation and location, and reliability of measurement. Conditional logistic regression was conducted to assess associations between these global measures of methylation and gastric cancer risk, adjusting for Helicobacter pylori and other potential confounders. We tested non-linear associations using quintiles of the global measure distribution. A genome-wide association study of DNA methylation and gastric cancer risk was also conducted (N=484,989 CpGs) using conditional logistic regression, adjusting for potential confounders. Differentially methylated regions (DMRs) were investigated using the R package DMRcate. We found no evidence of associations with gastric cancer risk for individual CpGs or DMRs (p> 7.6×10-6). No evidence of association was observed with global measures of methylation (Odds ratio (OR) 1.07 per SD of overall median methylation, 95% CI 0.80-1.44, p=0.65). We found no evidence that blood DNA methylation is prospectively associated with gastric cancer risk.