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Diabetic men with prostate cancer lived significantly longer and were significantly less likely to die of prostate cancer when treated with metformin, an insulin-lowering drug, according to the results of a study published in Journal of Clinical Oncology.

Prostate cancer is the most commonly diagnosed cancer (other than skin cancer) in U.S. men. Each year, more than 240,000 men are diagnosed with the disease.

Approximately 25.8 million people in the United States have diabetes, according to the U.S. Centers for Disease Control and Prevention. Nearly 95 percent of diabetes cases are type 2 diabetes, which is a disease characterized by insulin resistance. Insulin is a hormone that helps regulate the level of glucose (sugar) in the body. With type 2 diabetes, the body’s ability to make and use insulin deteriorates. Metformin is a widely prescribed drug that increases insulin sensitivity and is commonly used to treat type 2 diabetes.

Researchers performed a population-based, retrospective cohort study to examine the relationship between the use of antidiabetic medication use and all-cause and prostate cancer-specific mortality. The study included 3,837 patients over the age of 66 with incident diabetes who subsequently developed prostate cancer.

During a median follow-up of 4.64 years, 1,343 patients died, and 291 of these deaths were attributed to prostate cancer. Medical records indicated that 1,251 men were treated with metformin before prostate cancer diagnosis and 1,619 were treated with metformin after diagnosis. Treatment with metformin lasted a median of 19 months before prostate cancer diagnosis and 8.9 months after diagnosis.

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The data indicated that cumulative duration of metformin use after a prostate cancer diagnosis was associated with a significant reduction in the risk of both prostate cancer-specific death and all-cause death in a dose-dependent fashion. Each 6 months of metformin use was associated with a 24 percent reduction in prostate cancer-specific mortality compared with men who did not receive metformin. During the first 6 months of metformin use, men had a 24 percent lower all-cause mortality, but this decreased to 7 percent after 24 to 30 months of metformin treatment. Among 850 men receiving treatment with metformin alone, each additional 6 months of treatment was associated with a 44 percent reduction in the risk of prostate cancer-specific mortality and a 20 percent reduction in all-cause mortality. The benefits in mortality were unaffected by the type of cancer therapy. What’s more—cumulative use of other diabetes drugs did not significantly affect all-cause or prostate cancer-specific mortality.

The researchers concluded that metformin use after a prostate cancer diagnosis was associated with a reduction in all-cause and prostate cancer-specific mortality among diabetic men.


Margel D, Urbach DR, Lipscombe LL, et al. Metformin use and all-cause and prostate cancer–specific mortality among men with diabetes. Journal of Clinical Oncology. Published early online August 5, 2013. doi: 10.1200/JCO.2012.46.7043

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