Metformin Doesn’t Decrease Bladder Cancer in Diabetes Patients

By Brenda L. Mooney

PHILADELPHIA – Use of metformin does not decrease the incidence of bladder cancer in patients with diabetes, according to a study looking at new users of drug therapies.

The study, published recently in Diabetes Care, found that patients using metformin had similar bladder cancer risk as those using sulfonylureas . Both types of drugs carry a lower risk of bladder cancer than thiazolidinediones (TZD), according to background in the article.1

The research was led by Ronac Mamtani, MD, MSCE, assistant professor of medicine at the Hospital of the University of Pennsylvania and attending physician in hematology-oncology at the Philadelphia VAMC.

Study authors note that previous investigations evaluating the effect of metformin on cancer risk were affected by time-related biases. “To avoid these biases,” they write, “we examined the incidence of bladder cancer in new users of metformin and sulfonylureas (SUs).”

Focus on New Users

The study included 87,600 patients with type 2 diabetes who were part of the Health Improvement Network database in the UK.  With diabetes patients at a slightly increased risk of bladder cancer over time, researchers focused only on patients who were new users of either metformin or SUs.

In the study group, 196 incident bladder cancer cases were identified in the metformin cohort and 66 cancers in the SU cohort between July 2000 and August 2010. Use of metformin was not associated with decreased bladder cancer risk (HR 0.81 [95% CI 0.60–1.09]), and the association did not differ by sex (P for interaction = 0.20).

In addition, no association was observed with duration of metformin relative to SU use (3 to less than 4 years of use: 0.57 [0.25–1.34]; 4 to less than 5 years of use: 0.93 [0.30–2.85; greater than or equal to 5 years of use: 1.18 [0.44–3.19]; P for trend = 0.26).

Results were adjusted for age, sex, smoking, obesity, and HbA1c level.

“Use of metformin is not associated with a decreased incidence of bladder cancer,” the authors conclude, recommending, “Similar methods should be used to study other cancers that have previously been identified as potentially preventable with metformin.”

Metformin, the most commonly prescribed diabetes drugs, has been linked in observational studies with reduction in a variety of cancers affecting the breast, colon, liver, lung and pancreas. Two recent meta-analysis also indicated an overall 30% decrease in risk of all cancers with use of metformin compared to other diabetes therapies.

Mamtami led an earlier study, published in 2012, that found that TZD therapy lasting five years or longer appeared to put patients with type 2 diabetes at increased risk of bladder cancer.

1.Mamtani R,  Pfanzelter N, Haynes K, Finkelman BS, et. al. Incidence of Bladder Cancer in Patients With Type 2 Diabetes Treated With Metformin or Sulfonylureas. Published online before print February 4, 2014, doi: 10.2337/dc13-1489 Diabetes Care February 4, 2014

2Mamtani R, Haynes K, Bilker WB, Vaughn DJ, Strom BL, Glanz K, Lewis JD. Association between longer therapy with thiazolidinediones and risk of bladder cancer: a cohort study. J Natl Cancer Inst. 2012 Sep 19;104(18):1411-21. Epub 2012 Aug 9. PubMed PMID: 22878886; PubMed Central PMCID: PMC3529598.

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