Researcher say their mice study suggests widely used diabetes drug Metformin also reduces the risk of cancer.

The drug used on mice exposed to tobacco carcinogens was seen to reduce the development of lung tumours by over 70%. Results from a small clinical trial in Japan indicated it also reduced the rates of colorectal tumours in humans. Clinical trials are now being organised by the National Cancer Institute for testing the drug on those who smoke, including testing it against breast and prostate cancer.

Researchers say there is insufficient evidence to use metformin routinely for cancer prevention, however, it is strong enough for doctors considering it as drug therapy for type 2 diabetes to lean toward metformin, because of its supplementary effects.

Recent research on metformin published in the journal Cancer Prevention Research shows the drug to be particularly promising, as unlike the use of finasteride for preventing prostate cancer, or tamoxifen for breast cancer, metformin acts across a broad spectrum of cancers.

Known to increase the sensitivity of cells to insulin, it is among the most widely used diabetes drugs, with 40 million prescriptions written in USA in 2008.

In addition, it also has a number of other biological effects, such as, inhibiting a key signaling process between receptors in cells and reducing circulating levels of insulin and insulin-like growth factor, all of which actions inhibit or prevent the growth of cancer cells.

A 2005 observational study in Britain stimulated interest in metformin, after it found diabetics taking metformin had a 40% lower risk of cancer, a fact substantiated by subsequent studies.

Metformin was developed from the French lilac plant, which was known in the Middle Ages to control excess urination, a symptom of uncontrolled diabetes. FDA approved the drug in the mid-1990s.