Background: Increasing evidence suggests that diabetes mellitus (DM) may be associated with an increased risk of bladder cancer. To provide a quantitative assessment of this association, we evaluated the relation between DM and incidence and mortality of bladder cancer in an updated meta-analysis of cohort studies. Methods We identified cohort studies by searching the EMBASE and MEDLINE databases, through 31 March 2012. Summary relative risks (RRs) with 95% confidence intervals (CIs) were calculated with random-effects models.
Results: A total of 29 cohort studies (27 articles) were included in this meta-analysis. DM was associated with an increased incidence of bladder cancer (RR 1.29, 95% CI: 1.08-1.54), with significant evidence of heterogeneity among these studies (p<0.001, I(2) = 94.9%). In stratified analysis, the RRs of bladder cancer were 1.36 (1.05-1.77) for diabetic men and 1.28 (0.75-2.19) for diabetic women, respectively. DM was also positively associated with bladder cancer mortality (RR 1.33, 95% CI: 1.14-1.55), with evident heterogeneity between studies (p = 0.002, I(2) = 63.3%). The positive association was observed for both men (RR 1.54, 95% CI: 1.30-1.82) and women (RR 1.50, 95% CI: 1.05-2.14).
Conclusion: These findings suggest that compared to non-diabetic individuals, diabetic individuals have an increased incidence and mortality of bladder cancer.