Background: Low global methylation levels measured in post-diagnostic case compared to healthy control blood DNA have been associated with elevated bladder cancer risk.

Objective: To examine this association using blood DNA collected prior to bladder cancer diagnosis.

Methods: Cases (n=437) and controls (N=847) were selected from the Prostate, Lung, Colorectal, Ovarian Cancer Screening Trial (PLCO). A replication case-control study was conducted among males from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) cohort (391 cases/778 controls). LINE-1 percent 5-methyl-cytosine (LINE-1 %5-MeC) levels were quantified using bisulfite treated blood DNA and pyrosequencing. Cancer risk was assessed in deciles (D1-D10: 10-100%) and quartiles (Q1-Q4:25-100%) of methylation levels based on controls. Logistic regression was used to evaluate individual and pooled study data.

Findings: In PLCO, significantly lower bladder cancer risk was associated with the lowest LINE-1 %5-MeC decile (D1) compared to D2-D10 subjects adjusted for sex and pack-years of smoking (OR=0.35; 95% CI: 0.18-0.68, p=0.002). Findings were corroborated in the ATBC study, (D1 vs. D2-D10: OR=0.31;95% CI:0.17-0.57, p<0.001) adjusting for pack-years of smoking and intervention assignment. When male data were pooled, a similar association was observed comparing D1 to D2-D10 subjects (OR=0.35;95% CI:0.21-0.57, p<0.001) and by quartiles (OR Q1=0.53;95% CI:0.41-0.70, p<0.001). Smoking status did not modify the associations.

Interpretation: Findings observed in two independent studies using pre-diagnostically collected bladder cancer case/control subject DNA support that higher methylation levels may reflect higher bladder cancer risk prior to diagnosis. Associations using pre-diagnostically collected blood DNA were opposite to those from previous case-control studies using post-diagnostic DNA, suggesting changes in methylation levels associated with the carcinogenic process. Additional prospective studies evaluating LINE1 and gene-specific CpG methylation levels are needed to replicate and extend these findings.

This proffered talk is also presented as Poster 11.

Citation Format: Gabriella Andreotti, Sara Karami, Ruth Pfeiffer, Lauren Hurwitz, Linda Liao, Stephanie Weinstein, Demetrius Albanes, Jarmo Virtamo, Debra Silverman, Nathaniel Rothman, Lee Moore. LINE-1 %5-methyl cytosine levels in prediagnostic leukocyte DNA and future bladder cancer risk among PLCO and ATBC cohort subjects. [abstract]. In: Proceedings of the AACR Special Conference on Post-GWAS Horizons in Molecular Epidemiology: Digging Deeper into the Environment; 2012 Nov 11-14; Hollywood, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(11 Suppl):Abstract nr PR1.