(HealthDay News) – Limited evidence supports an increased risk of bladder cancer in adults with type 2 diabetes treated with thiazolidinediones, specifically pioglitazone, according to a review and meta-analysis published online July 3 in CMAJ, the journal of the Canadian Medical Association.

Isabelle N Colmers, of the University of Alberta in Edmonton, Canada, and colleagues performed a systematic review and meta-analysis of four randomized controlled trials (RCTs), five cohort studies, and one case-control study. The studies evaluated the risk of bladder cancer in adults with type 2 diabetes who were treated with thiazolidinediones, including pioglitazone or rosiglitazone.

The researchers identified 3,643 newly diagnosed cases of bladder cancer among the 2,657,365 patients who participated in the studies, for an overall incidence of 53.1 per 100,000 person-years. The cohort studies showed an increased risk of bladder cancer with thiazolidinedione treatment (pooled risk ratio [RR], 1.15), specifically pioglitazone (pooled RR, 1.22). However, no significant correlation was observed with bladder cancer in the one RCT that assessed pioglitazone (RR, 2.63; 95% confidence interval [CI], 0.91–6.13) or the two RCTs that assessed rosiglitazone (pooled RR, 0.87; 95% CI, 0.34–2.23).

“Although the absolute risk of bladder cancer associated with pioglitazone was small, other evidence-based treatments for type 2 diabetes may be equally effective and do not carry a risk of cancer,” the authors write. “This study quantifies the association between pioglitazone use and bladder cancer and may help inform decisions around safer use of pioglitazone in individuals with type 2 diabetes.”

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