Not surprisingly, metformin also decreased blood sugar levels, insulin growth factor and body mass index (BMI, a measure of obesity).
None of the men in the study had diabetes, said Joshua, so "it remains to be seen who would benefit the most from metformin." The most appropriate patients may be those with diabetes, those who are at risk for the disease or those whose tumors are sensitive to metformin.
It's unclear exactly how metformin exerts its effect but it may reduce the amount of circulating insulin in the blood, and insulin can fuel the growth of prostate cancer cells, explained Joshua.
The drug may also interfere with a specific pathway linked to cancer growth, he added.
The results build on prior research done in the laboratory but are the first to be seen in humans. Experts note, however, that research presented at medical meetings is typically considered preliminary until published in peer-reviewed journals.
In another study, researchers at the University of Texas M.D. Anderson Cancer Center in Houston, reviewed records of 302 patients who had both diabetes and pancreatic cancer, two conditions that often go hand-in-hand. A total of 117 patients were taking metformin.
About 30 percent of those who had taken the drug were alive after two years, compared with 15.4 percent of those who had not taken metformin (the "control" group).
And patients on metformin lived an average of just over 15 months versus about 11 months for the control group, translating into a 32 percent reduced risk of dying.
But the survival benefit was seen only in patients whose cancer had not yet spread. The study was published in the journal Clinical Cancer Research.
"I think it's very hopeful," said Dr. Michael Pishvaian, assistant professor of
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