Common diabetes treatment may cause bladder cancer

By Sally Robertson, B.Sc.Aug 22 2012

A commonly used diabetes treatment may increase patients' risk for bladder cancer, show US study findings.

"The results from this study suggest that 5 or more years of exposure to thiazolidinediones (TZDs) may be associated with a higher incidence of bladder cancer than comparable exposure to SUs [sulfonylureas]," say Ronac Mamtani (University of Pennsylvania, Philadelphia) and colleagues.

The US Food and Drug Administration recently warned that use of pioglitazone may be associated with an increased risk for bladder cancer. The warning, however, was based on limited data from the Kaiser Permanente Northern California (KPNC) diabetes registry, the French national health information system, and the PROspective pioglitAzone Clinical Trial In macroVascular Events (PROactive) study, say the researchers.

"None of the previous studies directly compared the TZDs with the sulfonylureas (SUs), the common alternative therapy for Type 2 diabetes not adequately controlled with metformin," explain Mamtani et al.

Using The Health Improvement Network database, the team conducted a retrospective study of 59,855 patients with Type 2 diabetes who received a prescription for either a TZD or SU between July 2000 and August 2010.

As reported in the Journal of the National Cancer Institute, there were 197 incident bladder cancers diagnosed over 196,708 person-years of follow up, with incident rates of 87.1 and 107.2 per 100,000 person-years with TZD and SU use, respectively.

The team reports that there was no significant difference in risk for bladder cancer between TZD and SU users.

However, the risk was increased with longer time since initiation of TZD therapy. Those who initiated TZD therapy 5 years or more previously were at more than three times the risk for bladder cancer than those who had started treatment less than 1 year earlier.

The team also found that the increase in risk over time with TZD therapy was significantly greater for TZD use than with SU use. Those who initiated TZD therapy more than 5 years previously were more than twice as likely to develop bladder cancer than those who initiated SU therapy at the same time point.

"The reproducibility of the findings from the US and French studies, and now using UK data, provides support for the hypothesis that long-term treatment with the TZDs may be associated with an increased risk of bladder cancer relative to the common alternative therapy, an effect that does not seem unique to pioglitazone," warn Mamtani and team.

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