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. 2014 Jul;37(7):1910-7.
doi: 10.2337/dc13-1489. Epub 2014 Feb 4.

Incidence of bladder cancer in patients with type 2 diabetes treated with metformin or sulfonylureas

Ronac Mamtani  1 , Nick Pfanzelter  2 , Kevin Haynes  3 , Brian S Finkelman  3 , Xingmei Wang  3 , Stephen M Keefe  2 , Naomi B Haas  2 , David J Vaughn  2 , James D Lewis  3
Affiliations

Incidence of bladder cancer in patients with type 2 diabetes treated with metformin or sulfonylureas

Ronac Mamtani et al. Diabetes Care. 2014 Jul.

Abstract

Objective: Previous studies evaluating the effect of metformin on cancer risk have been impacted by time-related biases. To avoid these biases, we examined the incidence of bladder cancer in new users of metformin and sulfonylureas (SUs).

Research design and methods: This cohort study included 87,600 patients with type 2 diabetes in The Health Improvement Network database. Use of metformin or an SU was treated as a time-dependent variable. Cox regression-generated hazard ratios (HRs) compared metformin use with SU use, adjusted for age, sex, smoking, obesity, and HbA1c level.

Results: We identified 196 incident bladder cancers in the metformin cohort and 66 cancers in the SU cohort. Use of metformin was not associated with decreased bladder cancer risk (HR 0.81 [95% CI 0.60-1.09]). This association did not differ by sex (P for interaction = 0.20). We observed no association with duration of metformin relative to SU use (3 to <4 years of use: 0.57 [0.25-1.34]; 4 to <5 years of use: 0.93 [0.30-2.85; ≥5 years of use: 1.18 [0.44-3.19]; P for trend = 0.26).

Conclusions: Use of metformin is not associated with a decreased incidence of bladder cancer. Similar methods should be used to study other cancers that have previously been identified as potentially preventable with metformin.

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Figures

Figure 1
Figure 1
Study flow diagram. A retrospective cohort study was conducted among type 2 diabetes patients in the THIN database. We compared new users of metformin (MET) with new users of SUs and excluded patients with use of these drugs before 1 July 2000 or within 6 months of enrollment in THIN.
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