Background: Aberrant global DNA methylation is shown to increase cancer risk. LINE-1 has been proven a measure of global DNA methylation. The objectives of this study were to assess the association between LINE-1 methylation level and bladder cancer risk and to evaluate effect modification by environmental and genetic factors. Methods: Bisulphite-treated leukocyte DNA from 952 cases and 892 hospital controls was used to measure LINE-1 methylation level at four CpG sites by pyrosequencing. Logistic regression model was fitted to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs). Interactions between LINE-1 methylation levels and environmental and genetic factors were assessed. Results: The risk of bladder cancer followed a nonlinear association with LINE-1 methylation. Compared with subjects in the middle tertile, the adjusted OR for subjects in the lower and the higher tertiles were 1.26 (95% CI 0.99–1.60, P=0.06) and 1.33 (95% CI 1.05–1.69, P=0.02), respectively. This association significantly increased among individuals homozygous for the major allele of five single-nucleotide polymorphisms located in the phosphatidylethanolamine N-methyltransferase gene (corrected P-interaction<0.05). Conclusions: The findings from this large-scale study suggest that both low and high levels of global DNA methylation are associated with the risk of bladder cancer.

This work was supported by the Association for International Cancer Research (grant number 09-0780); Fondo de Investigación Sanitaria, Spain (grant numbers 00/0745, PI051436, PI061614, G03/174); Red Temática de Investigación Cooperativa en Cáncer (grant number RD12/0036/0050-RTICC), Spain; European Commission (grant numbers EU-FP7-HEALTH-F2-2008-201663-UROMOL; EU-FP7-HEALTH-F2-2008-201333-DECanBio); Fundación Científica de la AECC, Spain; US National Institutes of Health (grant number USA-NIH-RO1-CA089715); and the Intramural Research Program of the Division of Cancer Epidemiology and Genetics, National Cancer Institute at the National Institutes of Health, USA