Several recent studies have suggested unexpected benefits of metformin. This prompted a slew of meta-analyses looking for evidence of benefit in preventing cancer. This evidence needs to be interpreted with caution; this latest review, looking at liver cancer, is a case in point.
In type 2 diabetes, does metformin prevent liver cancer?
Five studies were found, involving 105,495 participants. When the data were pooled, metformin was found to be associated with a reduced risk of liver cancer. The odds ratio was 0.38 ( 95% confidence interval 0.24 to 0.59).
Users of this research should consider:
- Did the reviewers do enough to find all of the relevant studies?
- The reviewers included observational studies and did not look at controlled trials. This means that each individual study has a higher risk of bias.
- Treatment with metformin may indicate a less severe case of type 2 diabetes. There may be another common factor at play.
- It is hard to envisage an ethical controlled trial that would involve withholding treatment with metformin from people with type 2 diabetes to provide a comparison. Therefore, further high quality cohort studies, with adjustment for important confounding variables, are required to further investigate this link.
Zhang ZJ, Zheng ZJ, Shi R, Su Q, Jiang Q, Kip KE. Metformin for Liver Cancer Prevention in Patients with Type 2 Diabetes: A Systematic Review and Meta-Analysis. J Clin Endocrinol Metab. 2012 Apr 20. [Epub ahead of print]