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.
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.