Diabetes mellitus has been associated with an increased risk of bladder cancer, although the evidence is still open to discussion.

We examined this association using data from a multicentre Italian case-control study, conducted between 2003 and 2014 on 690 bladder cancer cases and 665 frequency-matched hospital controls. Odds ratios (ORs) for diabetes were estimated by unconditional multiple logistic regression models, after allowance for major known risk factors for bladder cancer.

One hundred and twelve (16.2%) cases and 57 (8.6%) controls reported a diagnosis of diabetes mellitus, corresponding to a multivariate OR of 2.09 (95% confidence interval (CI): 1.46-3.01). Bladder cancer risk increased with duration of diabetes (OR 1.92 for 1-<5 years, 1.63 for 5-<10 years, 2.39 for 10-<15 years, and 2.58 for ⩾15 years). The increased risk of bladder cancer was consistent in strata of age and education, whereas it was somewhat lower (although not significantly) in women (OR 1.18), in never (OR 1.31) and current (OR 1.42) smokers, and in subjects with a body mass index <25 kg m(-2) (OR 1.48).

The present study provides further support of a role of diabetes in bladder cancer aetiology, although some residual confounding by tobacco, body mass index, or other unmeasured covariates may partly explain the association observed.British Journal of Cancer advance online publication 21 May 2015; doi:10.1038/bjc.2015.178 www.bjcancer.com.