Genome-wide DNA methylation in pre-diagnostic blood and bladder cancer risk in the Women's Health Initiative

Abstract

Background: Differential DNA methylation as measured in blood is a promising marker of bladder cancer susceptibility. However, previous studies have exclusively used post-diagnostic blood samples, meaning that observed associations may be markers of disease rather than susceptibility. Methods: Genome-wide methylation was measured in pre-diagnostic blood samples, using the Illumina Infinium HumanMethylation450 Bead Array, among 440 bladder cancer cases with the transitional cell carcinoma (TCC) subtype and 440 matched cancer-free controls from the Women's Health Initiative (WHI) cohort. After normalization and probe filtering, we used conditional logistic regression models to test for associations between methylation measurements at 361,184 CpG sites and bladder cancer risk. Results: Increased methylation at cg22748573, located in a CpG island within the 5'-UTR/first exon of the CITED4 gene, was associated with an 82% decreased risk of bladder cancer after adjusting for race/ethnicity, smoking status, pack-years of smoking, and leukocyte cell profile and accounting for multiple testing (OR=0.18, q-value = 0.05). The result was robust to sensitivity analyses accounting for time between enrollment and diagnosis, race, tumor subtype, and secondhand smoke exposure. Conclusions: While results need to be confirmed in additional prospective studies, differential methylation in CITED4, as measured in blood, is a promising marker of bladder cancer susceptibility. Impact: Identification of biomarkers of bladder cancer susceptibility in easily accessible tissues may allow targeting of screening efforts so as to improve bladder cancer prognosis. This is particularly important among women, who tend to have poorer bladder cancer outcomes than men.