More than two years’ daily exposure to pioglitazone doubled the risk of bladder cancer in people with type 2 diabetes, research has shown. However, the authors of the study say today on bmj.com that absolute risks remain low – and they found no increase in risk with rosiglitazone.
Researchers from Canada used the UK’s General Practice Research Database to look for associations between the use of pioglitazone or rosiglitazone and the risk of bladder cancer in 115,727 people who became new users of diabetes medicines between 1988 and 2009.
The rate of bladder cancer in people who had ever taken pioglitazone was 74 per 100,000 person years; among those who had taken it for at least two years the rate was 88 per 100,000 person-years. The rate among people who had cumulatively taken 28,000mg or more was considerably higher, at 137 per 100,000 person-years. For comparison, the usual rate in the UK is 73 per 100,000 person-years in people at least 65 years old.
The study’s authors say 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 … While the magnitudes of the rate ratios were relatively high, the risks associated with pioglitazone are in absolute terms low.”
Nevertheless they warn doctors and patients to “be aware of this association when assessing the overall risks and benefits of this therapy”.
Authors of an accompanying editorial question, in some detail, why this association was not predicted sooner. The European Medicines Agency last year raised questions about links with bladder cancer, although suspicions had been raised much earlier.
They conclude: “Considering that the benefit of pioglitazone in reducing cardiovascular events is questionable, prescribers who are ultimately responsible for therapeutic choices can legitimately question whether the benefit-risk ratio of pioglitazone is still acceptable for their patients with diabetes.”