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A popular class of diabetes drugs called thiazolidinediones (TZDs) increases the risk of bladder cancer, according to the results of a study published early online in the Journal of the National Cancer Institute.

Bladder cancer is diagnosed in as many as 60,000 individuals annually in the United States. Individuals with diabetes are already at an increased risk of bladder cancer compared to the general population—and now the evidence appears to be mounting that TZDs further increase this risk. TZDs account for about 20 percent of the drugs prescribed to diabetics in the U.S.

Researchers from the Perelman School of Medicine at the University of Pennsylvania analyzed data from nearly 60,000 patients with type 2 diabetes from the Health Improvement Network (THIN) database in the United Kingdom. About one-third of the patients were treated with a TZD and the rest were treated with another class of diabetes drug called a sulfonylurea drug.

The results indicated that long-term use of TZDs was associated with an increased risk of bladder cancer. Patients taking TZDs for five or more years were two to three times more likely to develop bladder cancer compared to those who took sulfonylurea drugs. Among patients who took TZDs for that length of time, the analysis indicated that 170 out of 100,000 would develop bladder cancer, compared to 60 out of 100,000 who took sulfonylurea drugs.

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Diabetes is a growing epidemic and increased risk associated with a common class of drugs has serious implications. Previous studies have indicated that one drug in the TZD class, pioglitazone, was associated with an increased risk of bladder cancer; however, the new data indicates that the entire class of TZDs may actually be associated with an increased risk. This is one of the first studies analyzing the risk among people taking both types of TZDs compared to those taking sulfonylurea drugs.

The researchers concluded that long-term treatment (5 or more years) with TZDs may be associated with an increased risk of bladder cancer and the risk appears to be common among all TZDs. The mounting evidence indicating the risks of TZDs may help physicians and patients to weigh the risk and benefits when choosing diabetes medication.


Mamtani R, Haynes K, Bilker WB, et al. Association between longer therapy with thiazolidinediones and risk of bladder cancer: A cohort study. Journal of the National Cancer Institute. Published early online August 9, 2012. doi: 10.1093/jnci/djs328.