In older men with diabetes and prostate cancer, taking the diabetes drug metformin was linked to a lower risk of death, according to a new study.
Researchers found metformin's apparent benefits accumulated over time. Among men with diabetes in Ontario, Canada, who were over age 66, the study found a 24 percent reduction in prostate-cancer mortality for every six months of metformin use, and a similarly lower risk of death from any cause for the first six months.
"Among diabetic men with prostate cancer metformin should be considered the drug of choice, not only for diabetes control but possibly to improve prostate cancer outcomes," Dr. David Margel, a urologist at Rabin Medical Center, Petah Tikva, Israel, and lead author of the study, told Reuters Health in an email.
The World Health Organization estimates that prostate cancer is among the top five leading causes of cancer death worldwide.
Approximately 1 in 7 men in the U.S. will be diagnosed with prostate cancer at some point in their lives, with roughly two-thirds of these cases found between the ages of 55-74. According to the National Cancer Institute, more than 29,000 American men will die from prostate cancer in 2013.
Likewise, the World Health Organization estimates that 347 million people worldwide have diabetes, and that it will be the seventh leading cause of death by 2030.
According to the U.S. Centers for Disease Control and Prevention, more than 25 million Americans are affected by diabetes and over one-quarter of people older than age 65 have the disease.
How metformin would work in someone with prostate cancer but without diabetes is unknown, however. Margel's research team is planning a randomized controlled trial to see if metformin also improves prostate cancer outcomes for non-diabetic men.
"Metformin is cheap, safe and has minimal side effects among patients without diabetes and therefore may be an ideal drug for secondary prevention." Margel added.
Metformin is a first-line medication for the treatment of noninsulin dependent diabetes. It is one of the oldest and cheapest oral diabetes medications, with prices ranging from 16 to 83 cents per pill for the generic form. The most common side effects include digestive problems and headache.
Using the Ontario Diabetes Database and the Ontario Cancer Registry, the researchers identified 3,847 men who had already been diagnosed with diabetes before their prostate cancer was discovered between March 1, 1997 and March 31, 2008.
The researchers also looked at the Ontario Drug Benefit Database to determine length of men's metformin use, as well as other diabetes medications and statins, which are used to control high blood cholesterol. Then they looked at deaths from prostate cancer and other causes.
The men were followed for about four and a half years, during which time 35 percent of them died. Of these, 7 percent died from prostate cancer.
The researchers, who published their findings in the Journal of Clinical Oncology, found that men who took metformin over time had significantly longer survival than men who didn't take the drug, in terms of deaths from prostate cancer as well as other causes.
Metformin's role seemed to be unique, since other diabetes medications did not have the same effect.
Statin use was also tied to decreased mortality, but the researchers were not able to examine what was going on with their use more closely.
"This is a scientifically rigorous and well-done study, and provides some of the best evidence we have up to this point that metformin may be helpful in preventing the progression of prostate cancer," said Dr. Scott Eggener, associate professor of surgery and co-director of the prostate cancer program at University of Chicago Medicine.
He cautioned, though, that this study was based on observation of events after they happened, so it cannot provide the level of evidence needed to say whether everyone with prostate cancer should go on metformin.
Metformin's role in preventing prostate cancer is also still unclear. Eggener told Reuters Health that most studies so far suggest metformin doesn't play a role in preventing diabetic men from developing prostate cancer.
"Once you have prostate cancer, what the present study suggests is that metformin may prevent progression or minimize the rate of progression," Eggener, emphasized, "This could turn out to be a real legitimate advance in prostate cancer management."