Diabetes Drug Metformin Linked to Lower Lung Cancer Rate in Mice

A drug widely used to treat high blood sugar in type 2 diabetics may hold some promise in the prevention of tobacco-induced lung cancer, according to extremely preliminary findings in a mouse study. In the September issue of Cancer Prevention Research, researchers report that metformin was associated with a substantial reduction (up to 73 percent) in the number of tumors mice developed when they were given a common carcinogen found in tobacco. Despite the fact that there have been no randomized controlled trials on whether metformin really can prevent cancer, researchers expressed excitement both over this animal study and previous epidemiological evidence pointing to this possibility.

Metformin has been in use for more than two decades and is currently prescribed to 40 million Americans. "This is a very safe agent and has been around for a while," said Cancer Prevention Research editor-in-chief Dr. Scott Lippman, chair of thoracic head and neck medical oncology at the University of Texas M.D. Anderson Cancer Center in Houston, at a Wednesday news conference. "The evidence in diabetic humans is very convincing and very strong," added Dr. Phillip Dennis, a senior investigator with the U.S. National Cancer Institute and senior author on the lung cancer paper. "Almost every epidemiological study I can think of found a decreased cancer incidence in diabetics taking metformin. The reduction is real and ranges from 30 to 70 percent."

The researchers thought metformin's possible cancer-lowering properties suggested the need for clinical trials to investigate whether the drug might help prevent tumors in smokers at high risk of developing cancer. Others believed that the finding might influence the choice of drugs in people with diabetes. "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 approval for metformin for cancer indications."