Pioglitazone May Increase Bladder Cancer Risk

Patients taking pioglitazone for type 2 diabetes may be at increased risk of bladder cancer, according to a study in the British Medical Journal.

The analysis included data on nearly 116,000 British primary care patients who started oral hypoglycemic drug treatment for type 2 diabetes from 1988 through 2009. During mean follow-up of 4.6 years, there were 470 diagnosed cases of bladder cancer: incidence rate 89.4 per 100,000 person-years. In a case-control study, 376 patients with bladder cancer diagnosed more than one year after starting treatment were matched to up to 20 controls.

Any pioglitazone exposure was associated with an increased risk of bladder cancer: rate ratio 1.83. Risk increased with both duration of treatment and total exposure to pioglitazone: rate ratio 1.99 for more than 24 months of treatment and 2.54 for a cumulative dosage greater than 28,000 mg. Patients taking rosiglitazone showed no increase in bladder cancer risk.

The study supports previous, limited data suggesting an increased incidence of bladder cancer among patients taking pioglitazone. The association appears specific to pioglitazone and appears to increase along with treatment duration and total drug exposure over time. The researchers emphasize that, although the relative risk of bladder cancer is about twice as high in patients taking pioglitazone, the absolute excess risk is low: adjusted rate difference 74 per 100,000 person years [Azoulay L, et al. The use of pioglitazone and the risk of bladder cancer in people with type 2 diabetes: nested case-control study. BMJ 2012; 344: e3645].