PhotoNearly 20 percent of the drugs prescribed to treat Type 2 diabetes may put those patients at increased risk of bladder cancer.

That's the conclusion of a new study in the Journal of the National Cancer Institute.

Researchers from the Perelman School of Medicine at the University of Pennsylvania found that patients taking thiazolidinedione, better known as TZD drugs, are two to three times more likely to develop bladder cancer than those who took a sulfonylurea drug, another common class of medications for diabetes.

Already at elevated risk

Not only is this a significant increase in the risk factor, but the researchers say people with diabetes are already at increased risk of developing bladder cancer compared to the general population.

Among the general population about 30 in 100,000 people develop bladder cancer. Among diabetes patients overall, the incidence of this cancer is typically about 40 out of 100,000.

The study is a major one, analyzing 60,000 Type 2 diabetes patients from the Health Improvement Network (THIN) database in the United Kingdom. They found that patients treated with the TZD drugs pioglitazone (Actos) or rosiglitzaone (Avandia) for five or more years had a two-to-three-fold increase in risk of developing bladder cancer when compared to those who took sulfonylurea drugs.

Risk sharply lower with sulfonylurea drugs

Patients taking TZDs for five or more years developed bladder cancer at a rate of 170 per 100,000. That compares with a rate of 60 in 100,000 for those who take sulfonylurea drugs -- such as glipizide (Glucotrol).

Diabetes afflicts 285 million people worldwide and the number is growing, thanks in part to increasing obesity.

“There are many factors clinicians must weigh in deciding which drug to use to control a patient’s diabetes, and these new data provide important information to include in that decision-making process,” said the study’s lead author, Ronac Mamtani, MD, an instructor in the division of Hematology-Oncology in Penn’s Abramson Cancer Center. “Our study shows that doctors who care for patients with diabetes should be very aware of any bladder-related symptoms patients might be having, like blood in the urine, and take steps to further evaluate those issues.”

Ninth most prescribed drug in U.S.

In recent years Avandia has fallen out of favor in the U.S. as it has been linked to heart attacks in some studies. Actos, meanwhile, is the ninth most commonly prescribed drug in the nation, accounting for some 15 million prescriptions each year.

The drug is often prescribed when Type 2 diabetes patients’ illnesses can no longer be controlled with the first-line diabetes drug Metformin.

Based on previous data examining safety risks among patients taking Actos, the FDA has already warned that it may be associated with a risk of bladder cancer, and France and Germany have removed the drug from their markets.

The authors say their findings add to mounting evidence against the entire class of TZDs, as one of the first studies examining this type of risk among people taking both types of TZDs and among those taking sulfonylurea drugs.

Patients currently taking a TZD to treat Type 2 diabetes should discuss the risk-benefit trade-off with their doctor.

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