Metformin may reduce the risk of cancer, but more research is needed

This systematic review looked at the relationship between oral antidiabetic drugs and the risk of cancer.

Clinical question:

In type 2 diabetes, does treatment with metformin or sulphonylurea affect the risk of cancer?

The evidence:

The reviewers found 17 observational studies reporting 37,632 cases of cancer.  When they pooled the data from these studies they found that use of metformin, but not sulphonylureas, was associated with a reduced risk of subsequent cancer.

The results were statistically significant for colorectal and pancreatic cancer, but not breast or prostate cancer.

Appraisal hints:

  • The literature search was inadequate, only focusing on MEDLINE.  It is likely that other studies have been carried out that were not found by the reviewers.
  • They found evidence of publication bias, suggesting that there may be unpublished negative trials.
  • It is not clear what the comparison is in this analysis.  What is the baseline risk against which metformin is being compared?  It seems likely that metformin may be acting as a marker of less severe disease.
  • The reviewers noted considerable heterogeneity between the studies.
  • Further prospective research is needed to reduce the uncertainty around this topic.


Soranna D, Scotti L, Zambon A, Bosetti C, Grassi G, Catapano A, La Vecchia C, Mancia G, Corrao G.   [Epub ahead of print]. Cancer Risk Associated with Use of Metformin and Sulfonylurea in Type 2 Diabetes: A Meta-Analysis.  Oncologist. 2012 May 29.

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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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