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Metformin May Lower Risk of Prostate Cancer Death

Diabetic men using the drug had higher survival rates in cancer study


During roughly four years of follow-up, Margel found those who took metformin had a 24 percent reduction in risk from prostate cancer death for every additional six months of use after their cancer diagnosis. The risk reduction of death from other causes was initially the same but declined over time.

In both instances, although an association was found between metformin and survival, a direct cause-and-effect relationship was not established.

No reduction in death risk was seen for patients taking any other diabetes drug.

Although other diabetes drugs work by increasing the body's insulin production, metformin is an "insulin sensitizer" that works by making the body more sensitive to the insulin already produced. Insulin is needed to move glucose into cells for energy.

Some research suggests that high insulin levels can influence cancer growth. Metformin, by not increasing the body's insulin production, may decrease cancer cells' growth, some experts say.

Typical side effects of the drug are mild diarrhea and stomach problems, Margel said. "Usually they subside after one or two weeks," he said.

In their next study, the researchers plan to test metformin in patients with prostate cancer but not diabetes. "Metformin is very safe to use among nondiabetic patients," Margel said.

The findings point to a need for a large study in which men with early stage prostate cancer are assigned to a metformin group or placebo group, one expert said. Writing in an accompanying journal editorial, Kathryn Penney, an instructor in medicine at Brigham and Women's Hospital in Boston, said at least nine ongoing trials are looking at metformin in men with recurrent or advanced prostate cancer.

But these current trials might be starting too late, she said. Instead, a trial should look at metformin's effect at the time of diagnosis, when the disease is typically in early stages.

"If this trial showed a benefit, then yes, men without diabetes could be put on metformin at the time of prostate cancer diagnosis," she said.

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