In type 2 diabetes, use of metformin was associated with lower incidence of colorectal cancer.

The chemical structure of metformin

Laboratory research has suggested that metformin may inhibit cancer cell growth.  If it does, we would expect people treated with metformin to have a lower rate of cancer.

This systematic review combined the data from five observational studies of patients with type 2 diabetes and studied the relationship between their use of metformin and incidence of colorectal cancer.

They found significantly lower rates of colorectal cancer among patients taking metformin compared with those who do not take it.

Appraisal hints

Users of this evidence are advised to consider the following:

  • It is not clear what types of patients were included in the meta-analysis.
  • It is not clear whether treatment with metformin is causing the reduction in risk, or some other factor, such as severity of diabetes, other medication or an unknown factor.
  • What quality assessments were made of the source data from observational studies.


Zhang ZJ, Zheng ZJ, Kan H, Song Y, Cui W, Zhao G, Kip KE. Reduced Risk of Colorectal Cancer With Metformin Therapy in Patients With Type 2 Diabetes: A meta-analysis. Diabetes Care. 2011 Oct;34(10):2323-8.


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I am an information scientist with an interest in making knowledge from systematic research more accessible to people who need it. This means you. I've been attempting this in the area of Evidence-Based Health Care since 1995. So far the results have been mixed. For some reason we expected busy clinicians to search databases and appraise papers instead of seeing patients. We also expected publishers to make the research freely available to the people who paid for it.. Ha! Hence The National Elf service.

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