Blood Leukocyte Methylation and Risk of Non-smoking-associated Cancer: A Case-cohort Study of Non-Hodgkin Lymphoma.

Unlabelled: Aryl-hydrocarbon receptor repressor () hypomethylation in peripheral blood is tightly linked with tobacco smoking and lung cancer. Here, we investigated methylation in non-Hodgkin lymphoma (NHL), a non-smoking-associated cancer. In a case-cohort study within the population-based Danish Diet, Cancer and Health cohort, we measured (cg23576855) methylation in prediagnostic blood from 161 participants who developed NHL within 13.4 years of follow-up (median: 8.5 years), with a comparison group of 164 randomly chosen participants. We measured DNA-methylation levels using bisulfite pyrosequencing and estimated incidence rate ratios (IRR) using Cox proportional hazards models with adjustment for baseline age, sex, educational level, smoking status, body mass index, alcohol intake, physical activity, and diet score. Global DNA-methylation levels were assessed by long interspersed nucleotide element 1 (LINE-1) analysis. Overall, the IRR for hypomethylation (lowest vs. other quartiles) was 2.52 [95% confidence interval (CI), 1.24-5.15]. When stratified according to time between blood draw and diagnosis, low methylation levels were associated with a future diagnosis of NHL [IRR: 4.50 (95% CI, 1.62-12.50) at 0-<5 years, 7.04 (95% CI, 2.36-21.02) at 5-<10 years, and 0.56 (95% CI, 0.21-1.45) at ≥10 years]. There was no association between global DNA-methylation levels and risk of NHL. Our results show that hypomethylation in blood leukocytes is associated with a higher risk of NHL in a time-dependent manner, suggesting that it occurs as a response to tumor development.

Significance: Our population-based study demonstrated that lower methylation levels in peripheral blood leukocytes were associated with an increased risk of NHL. This association was independent of tobacco smoking, sex, and lifestyle characteristics, but was highly dependent on time to diagnosis. These findings highlight the potential of methylation as a biomarker for NHL risk, effective up to 10 years after blood draw.