No Bladder Cancer Risk from Diabetes Drug?

bladder cancer and diabetes drug

For years, many experts have believed there was a risk of developing bladder cancer from use of the diabetes drug pioglitazone, based on the findings of both animal and human studies. Now the authors of an international decade-long study report there is no link between this medication and bladder cancer.

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This postmarketing study was conducted by Takeda, the manufacturer of pioglitazone, and the results were submitted to a variety of regulatory authorities, including the Food and Drug Administration (FDA). Although a five-year interim analysis of the data showed a statistically significant increased risk of bladder cancer among patients who had used pioglitazone (Actos) for more than two years, the 10-year analysis did not demonstrate that increased risk.

Here are some facts and findings concerning the new study:

  • The study population involved 1.01 million people with type 2 diabetes who lived in six locations throughout the world: British Columbia, Finland, Manchester (UK), Rotterdam (Netherlands), Scotland, and 566 general practices in the United Kingdom
  • A total of 3,248 cases of bladder cancer were identified
  • Only 117 individuals with bladder cancer had ever been exposed to pioglitazone
  • Median follow-up period was 4.0 to 7.4 years
  • No link between bladder cancer risk and the length of time patients used pioglitazone
  • No link between bladder cancer risk and an increased cumulative dose of the drug
  • No link between developing bladder cancer and the time since starting to take pioglitazone

How this study differs from past studies
In the past, studies have come up with conflicting results. A University of Pennsylvania study, for example, showed a twofold to threefold increased risk of bladder cancer among people who used pioglitazone for five years or longer when compared with patients who took another common medication (sulfonylurea) for diabetes.

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Another recent study, appearing in the Indian Journal of Endocrinology and Metabolism, is among those on the other side of the aisle. The investigative team in this study found no link between use of pioglitazone and bladder cancer.

The authors of the postmarketing study say their work differs from that of earlier attempts because they took steps to eliminate bias. For example, they noted that in some previous studies, the participants given pioglitazone were already at an increased risk of bladder cancer or that testing procedures introduced a detection bias.

Therefore the authors concluded that “our large international analysis does not support a causal effect of pioglitazone on bladder cancer, thus contradicting previous studies deemed to have proven this relationship.” This study is not necessarily the last word, however. The investigators also stated that further evaluations with longer follow-up and efforts to minimize bias were necessary to completely resolve the controversy.

SOURCES
Balaji V et al. A retrospective study on finding correlation of pioglitazone and incidences of bladder cancer in the Indian population. Indian Journal of Endocrinology and Metabolism 2014 May; 18(3): 425-27
Levin D et al. Pioglitazone and bladder cancer risk: a multipopulation pooled cumulative exposure analysis. Diabetologia 2014; DOI:10.1007/s00125-014-3456-9
Mamtani R et al. Association between longer therapy with thiazolidinediones and risk of bladder cancer: a cohort study. Journal of the National Cancer Institute 2012 Aug 9

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