Purpose: Studies have indicated that diabetes mellitus (DM) is a risk factor for bladder cancer; however,not all evidence supports this conclusion. The aim of this meta-analysis was to collate and evaluate all primaryobservational studies investigating the risk of bladder cancer associated with DM.
Methods: The PubMed andGoogle Scholar databases were searched to identify studies that estimated the association of DM and bladdercancer. Summary effect estimates were derived using a random-effects meta-analysis model.
Results: A totalof 23 studies (8 case-control studies, 15 cohort studies) including 643,683 DM and 4,819,656 non-DM caseswere identified. Analysis of all studies showed that DM was associated with an increased risk of bladder cancercompared with non-DM overall (OR=1.68, 95% CI 1.32-2.13). Analysis of subgroups demonstrated this to bethe case in both case-control studies (OR=1.59, 95% CI 1.28-1.97, I2=58%) and cohort studies (RR=1.70, 95%CI 1.23-2.33, I2=96%). There was no gender difference in DM-associated bladder cancer risk. Bladder cancerrisk was increased in Asia and the North America region, but not in Europe. Furthermore, DM-associatedbladder cancer risk was obviously higher in Asia than North America and Europe or in those with Caucasianethnicity. With extension of follow-up time, the bladder cancer risk was not increased for the patients with DM.
Conclusions: This meta-analysis provided further evidence supporting theDM association with a signiﬁcantlyhigher risk of bladder cancer obtained from observational studies.