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Metformin May Improve Survival Rates in Patients with Both Cancer and T2DM

Drug has demonstrated direct antitumor activity in mouse models…. 

Between 8 and 18 percent of cancer patients also have diabetes. This is likely due to the shared risk factors between the diseases. There is a higher incidence of cancer and cancer related mortality in patients with concurrent diabetes. Metformin is a very common medication prescribed to patients for the management of type 2 diabetes. Therefore, it is suggested that effectively controlling diabetes may protect against cancer development.

The use of metformin in type 2 diabetic patients is highly lauded because of its ability to inhibit hepatic gluconeogenesis, reduce insulin resistance, and decrease inflammatory response, all of which are potential tumor promoting activities. In several in vivo/vitro studies metformin has demonstrated direct antitumor activity by inducing cell cycle arrest and apoptosis, as well as suppressing xenograft tumor growth in mouse models. Furthermore, previous observational studies suggest that metformin is associated with reduced cancer risk and cancer mortality compared to other glucose lowering medications. However, although metformin shows potential as a cancer preventative medication compared to other diabetes medications, it is unclear whether it would be an effective medication for patients with an already established cancer diagnosis.

A meta-analysis was conducted using data from a pool of 20 English-written studies collected from Medline and PubMed that were published as of July 1, 2013. This represented a total of 13,008 patients with various cancer types and concurrent type 2 diabetes. The cancer types included pancreatic, colorectal, ovarian, breast, prostate, bladder, liver, larynx, and lung cancer. In these studies, metformin was associated with a significantly reduced death risk for those with pancreatic, colorectal, as well as other cancers (34% reduction of death risk) compared with non-metformin users, and a non-significantly reduced death risk for those with lung, prostate, and breast cancer compared with non-metformin users.

The researchers concluded that there is evidence that the use of metformin is associated with improved overall survival and cancer specific survival in the treatment of patients with type 2 diabetes and cancer.

This study shows the potential metformin may have as a first line drug of choice over other diabetic medications in treating both diabetes and cancer, provided the patient has no contraindications to the medication. Additional studies with larger samples sizes and different study designs are needed to strengthen the conclusion of this study. However, this study should not be interpreted to mean that metformin has definite therapeutic efficacy.

Practice pearls: 
  • Metformin showed antitumor activities in a substantial number of studies.
  • Reduction in risk of death was significant in patients with pancreatic and colorectal cancers, while lung, breast and prostate cancer was not statistically significant.
  • A cancer-preventative advantage associated with metformin does not necessarily imply effective therapeutic efficacy.

Yin, Min. et al. "Metformin Is Associated With Survival Benefit in Cancer Patients With Concurrent Type 2 Diabetes: A Systematic Review and Meta-Analysis." The Oncologist 18 (2013): 1-7