Global methylation in blood DNA has been associated with bladder cancer risk in case-control studies, but has not been examined prospectively. We examined the association between LINE1 total percent 5-methylcytosine and bladder cancer risk using pre-diagnostic blood DNA from the United States-based, Prostate, Lung, Colorectal, Ovarian Cancer Screening Trial (PLCO) (299 cases/676 controls), and the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) cohort of Finnish male smokers (391 cases/778 controls). Logistic regression adjusted for age at blood draw, study center, pack-years of smoking, and sex was used to estimate odd ratios (ORs) and 95% confidence intervals (CIs) using study- and sex-specific methylation quartiles. In PLCO, higher, although non-significant, bladder cancer risks were observed for participants in the highest three quartiles (Q2-Q4) compared with the lowest quartile (Q1) (OR = 1.36, 95% CI: 0.96 -1.92). The association was stronger in males (Q2-Q4 vs. Q1 OR = 1.48, 95% CI: 1.00-2.20) and statistically significant among male smokers (Q2-Q4 vs. Q1 OR = 1.83, 95% CI: 1.14-2.95). No association was found among females or female smokers. Findings for male smokers were validated in ATBC (Q2-Q4 vs. Q1: OR = 2.31, 95% CI: 1.62-3.30) and a highly significant trend was observed (P = 8.7 × 10(-7)). After determining that study data could be combined, pooled analysis of PLCO and ATBC male smokers (580 cases/1119 controls), ORs were significantly higher in Q2-Q4 compared with Q1 (OR = 2.03, 95% CI: 1.52-2.72), and a trend across quartiles was observed (P = 0.0001). These findings suggest that higher global methylation levels prior to diagnosis may increase bladder cancer risk, particularly among male smokers.
Keywords: ATBC; PLCO; bladder cancer; global methylation; nested case-control; pre-diagnostic blood DNA.