Patients with type 2 diabetes who are prescribed metformin appear to be at lower risk of cancer than those not treated with metformin. Lead author Dr. Josie M. M. Evans and colleagues at the University of Dundee in Scotland explain that metformin activates the enzyme AMP activated protein kinase, which in turn is regulated by the tumor suppressor LKB1. They therefore theorized that metformin use may reduce risk of cancer.
To test their hypothesis, they performed a case-control study in which a diabetes clinical information system was linked with a database of dispensed prescriptions.
Between 1993 and 2001, nearly 12,000 patients had been newly diagnosed with type 2 diabetes, including 923 who were later diagnosed with cancer. These were matched to 1846 diabetic subjects without cancer by age, year of diagnosis and gender.
During the year prior to the cancer diagnosis, 36.4% of cases and 39.7% of controls had been given a prescription for metformin (odds ratio 0.86). The odds ratio for any exposure to metformin since 1993 was 0.79.
There appeared to be a dose-response relationship between metformin and cancer, as the odds were further reduced by increasing duration of metformin treatment and total amount of metformin dispensed.
The research team is now in the planning phase of a large cohort study linked to a cancer registration database, they note.
BMJ Online First 2005.
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