Smokers developing lung cancer may get a cure in the common diabetes drug metformin, Reuter reports according to National Cancer Institute research findings on Wednesday. Metformin prevented lung tumor growth in mice exposed to a cancer-causing agent found in tobacco.

According to Dr Philip Dennis who led the research team Metformin switches on an enzyme that blocks mTOR -- a protein that helps tobacco-induced lung tumors grow.

They treated the mice with metformin either orally or with an injection. Mice that got the drug orally had 40 to 50 percent fewer tumors, while those injected with the drug had 72 percent fewer tumors.

The findings have encouraged the research team to continue the test in smokers.

Earlier studies have shown that metformin can cut diabetics' risk of pancreatic and breast cancers, which may be used as a cancer treatment drug in future.

According to the World Health Organization, tobacco is the leading preventable cause of death globally, killing more than 5 million people each year from heart disease, cancer and lung disease. The US Centers for Disease Control and Prevention estimates that 20 percent of US adults are smokers.