"All other things being equal, many diabetics face a choice of oral agents, and early evidence that metformin may have an effect on the oncology side may increasingly play a role in decision-making," said Dr. Michael Pollack, professor of medicine and oncology at McGill University in Montreal. "We can't ignore this, but we can't say we have FDA [U.S. Food and Drug Administration] approval for metformin for cancer indications."
Metformin was developed from the French lilac plant, known in the Middle Ages to control excess urination, a symptom of uncontrolled diabetes. The drug was approved by the FDA in the mid-1990s.
The study by Dennis and colleagues looked at mice that had been genetically engineered to be susceptible to lung tumors.
Mice taking metformin in their drinking water had 34 percent fewer tumors than those not taking metformin. And when the drug was administered by injection, the improvement seen was 73 percent.
Dennis stated that a likely mechanism of action resides in the liver "and specifically the hormones [including insulin] that are released." Insulin may have a relationship with cancer.
"It's most likely that metformin is working by reducing insulin and IGF1 [insulin-like growth factor] levels in the body," said Lewis Cantley, director of the Cancer Center at Beth Israel Deaconess Medical Center in Boston, and co-author of an accompanying perspective piece.
It's also possible, however, that metformin is working more directly on the tumor process, the researchers said.
A second study, this one a randomized controlled trial involving a very small number of humans (23), found that patients with an early form of colorectal cancer who were treated with metformin did see a decrease in possible cancer-related growth, compared with participants not taking the drug.
"These patients were not diabetic, so they didn't necessarily have high insulin levels to begin with but lower i
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