An increased risk of bladder cancer is linked to the use of pioglitazone, a medication commonly used to treat type 2 diabetes, according to a new study published in CMAJ (Canadian Medical Association Journal).

People with type 2 diabetes are at risk of several types of cancer, including a 40% increased risk of bladder cancer, compared to people without diabetes. Previous studies have shown a higher incidence of bladder cancer in people taking pioglitazone, a type of thiazolidinedione.

To determine whether there is a link between pioglitazone use and bladder cancer, researchers conducted a systematic review and meta-analysis of randomized controlled trials and observational studies involving over 2.6 million patients.

"We observed an increased risk of bladder cancer associated with the use of thiazolidinediones," writes Dr. Jeffrey Johnson, School of Public Health, University of Alberta, with coauthors. "In particular, use of pioglitazone was associated with an increased risk of bladder cancer based on a pooled estimate from three cohort studies involving more than 1.7 million individuals."

The researchers also looked at a possible association with rosiglitazone, another type of thiazolidinedione, but did not see an effect.

"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," conclude the authors. "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."