Type 2 diabetes mellitus,insulin‐use and risk of bladder cancer in a large cohort study

Type 2 diabetes mellitus (T2DM) is associated with increased bladder cancer incidence in some, but not all, studies. Many studies had limited statistical power and few examined risk by insulin‐use, duration of diabetes or cancer stage. We examined the association between T2DM and bladder cancer incidence in the Cancer Prevention Study II Nutrition Cohort, a large prospective study with information on insulin‐use and duration of diabetes. Diabetes and insulin‐use were ascertained from a questionnaire at study enrollment in 1992 or 1993 and updated in 1997 and every 2 years thereafter. During follow‐up through 2007, 1,852 cases of incident bladder cancer were identified among 172,791 participants. Multivariable adjusted relative risks (RRs) and 95% confidence intervals (CIs) were estimated using extended Cox regression modeling. There were no associations of T2DM with the risk of bladder cancer overall (RR = 1.01, 95% CI: 0.87–1.17), noninvasive disease (RR = 0.93, 95% CI: 0.76–1.14) or invasive disease (RR = 1.13, 95% CI: 0.91–1.40). Compared to participants without T2DM, risk of invasive bladder cancer was higher among participants who had had T2DM for >15 years (RR = 1.63, 95% CI: 1.09–2.43) and among those using insulin (RR = 1.64, 95% CI: 1.18–2.27). These results do not support an association of T2DM with overall bladder cancer incidence, but do suggest positive associations of long‐term T2DM and insulin‐use or other factors correlated with severe diabetes, with invasive bladder cancer incidence.