Does use of metformin protect against cancer in Type 2 diabetes mellitus?

J Endocrinol Invest. 2012 Feb;35(2):231-5. doi: 10.1007/BF03345423.


Background: Type 2 diabetes mellitus has been associated with an increased cancer risk, which can be modified by specific hypoglycemic drugs. In particular, metformin, the most frequently prescribed biguanide, is now considered a protective agent against cancer incidence and mortality in Type 2 diabetic patients.

Aims: To review the potential associations between metformin use and cancer incidence and mortality and the possible biological links implicated in these associations.

Materials and methods: We searched English-language original investigations published through September 2011.

Results: Metformin could block the mitogenic effects of insulin, but this effect does not entirely explain the reduction in cancer incidence. Metformin also plays a direct inhibition of cancer cell growth via the inhibitory effects of AMP-activated protein kinase on the mTOR pathway, which regulates cell growth and proliferation. Accordingly, many epidemiological studies have shown that metformin use is associated with a lower cancer incidence and mortality through a dose-response relationship, with greater exposure being associated with stronger risk reduction. Randomized clinical trials testing the effects of metformin on both recurrence and survival in early-stage breast cancer are on-going; these trials are based on pilot studies demonstrating an adjuvant effect of this drug in breast cancer.

Conclusions: Metformin is an inexpensive and safe drug, that may modify the increased cancer risk of Type 2 diabetic patients. On-going clinical trials will show whether this drug can enhance the effect of chemotherapy in the treatment of cancer.

Publication types

  • Evaluation Study
  • Review

MeSH terms

  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents / therapeutic use
  • Breast Neoplasms / complications
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / mortality
  • Carcinoma / complications
  • Carcinoma / epidemiology
  • Carcinoma / mortality
  • Clinical Trials as Topic
  • Diabetes Mellitus, Type 2 / complications
  • Diabetes Mellitus, Type 2 / drug therapy*
  • Diabetes Mellitus, Type 2 / epidemiology
  • Diabetes Mellitus, Type 2 / mortality
  • Female
  • Humans
  • Hypoglycemic Agents / pharmacology
  • Hypoglycemic Agents / therapeutic use
  • Metformin / pharmacology*
  • Metformin / therapeutic use*
  • Neoplasms / epidemiology
  • Neoplasms / mortality
  • Neoplasms / prevention & control*


  • Antineoplastic Agents
  • Hypoglycemic Agents
  • Metformin