Background: Whether rosiglitazone may increase bladder cancer risk has not been extensively investigated. Methods: The reimbursement databases of all Taiwanese diabetic patients under oral anti-diabetic agents or insulin from 1996 to 2009 were retrieved from the National Health Insurance. An entry date was set at 1 January 2006 and a total of 885,236 patients with type 2 diabetes were followed up for bladder cancer incidence till end of 2009. Incidences for ever-users, never-users and subgroups of rosiglitazone exposure (using tertile cutoffs of time since starting rosiglitazone, duration of therapy and cumulative dose) were calculated and hazard ratios estimated by Cox regression. Results: There were 102,926 ever-users and 782,310 never-users, respective numbers of incident bladder cancer 356 (0.35%) and 2753 (0.35%), and respective incidence 98.3 and 101.6 per 100,000 person-years. The overall hazard ratios (95% confidence intervals) did not show significant association in unadjusted model [0.969 (0.867, 1.082)] and models adjusted for age and sex [0.983 (0.880, 1.098)] or all covariates [0.980 (0.870, 1.104)]. Neither the P values for the hazard ratios for the different categories of the dose-responsive parameters, nor their P-trends were significant. Conclusions: Rosiglitazone does not increase the risk of bladder cancer.
