Pioglitazone, a drug used to treat type 2 diabetes, is associated with an increased risk of bladder cancer, according to findings from a study conducted by researchers from the Lady Davis Institute at the Jewish General Hospital, published in the British Medical Journal. The study was led by Dr. Laurent Azoulay of the Centre for Clinical Epidemiology, along with Hui Yin, Kristian B. Filion, Jonathan Assayag, Agnieszka Majdan, Michael N. Pollak, and Samy Suissa.
The results show that more than two years of daily exposure to pioglitazone doubles the risk of bladder cancer. However, the authors stress, in absolute terms, the risks are low – up to 137 extra cases per 100,000 person years. No increased risk was seen for a similar drug, rosiglitazone.
Pioglitazone and rosiglitazone belong to a class of drugs called thiazolidinediones, which help to control blood sugar levels in patients with type 2 diabetes. Both drugs are known to increase the risk of heart failure but, after carrying out a safety review, the European Medicines Agency decided to keep pioglitazone on the market.
Using a data base from the United Kingdom, the authors studied 115,727 patients newly treated with diabetes drugs from 1988 to 2009. Results showed that 470 patients were diagnosed with bladder cancer during the average 4.6 years of follow-up (a rate of 89 per 100,000 person years). The rate of bladder cancer in the general UK population aged at least 65 years is 73 per 100,000 person years.
If patients had ever taken pioglitazone they were at an 83% increased risk of bladder cancer. This corresponds to 74 per 100,000 person years. This increased to 88 per 100,000 person years for patients who had taken the drug for two years or more, and increased further to 137 per 100,000 years for patients who had taken 28,000 mg or more. These findings remained consistent in several further analyses designed to check the results.
The authors conclude that their results “provide evidence that pioglitazone is associated with an increased risk of bladder cancer, whereas no increased risk was observed with the thiazolidinedione rosiglitazone.”
They suggest that such associations may have been underestimated in previous observational studies and say doctors, patients, and regulatory agencies “should be aware of this association when assessing the overall risks and benefits of this therapy.”
Adapted from materials provided by McGill University