Diabetes drug may help fight breast cancer

They believe they work by blocking an enzyme behind two our of five cases of the cancer.

The drugs have already been tested for safety in clinical trials for their original use.

That means they could be fast-tracked into trials on breast cancer patients, and reach the market much more quickly. A brand new drug would take many years to research and develop.

The most common cancer in the UK, breast cancer affects more than 43,000 British women a year and claims more than 1,000 lives.

The scientists, from McGill University in Montreal, looked at the role an enzyme called PTP1B plays in breast cancer.

It is already known to be an important factor in diabetes and obesity, but it is also found in high levels in around 40 per cent of breast cancer patients.

Using mice genetically engineered to be prone to breast cancer, the researchers found that blocking production of the enzyme significantly slowed tumour development - and in some cases stopped tumours from forming altogether.

Cutting off the supply of the enzyme also stopped the cancer from spreading to the lungs.

Researcher Dr Michel Tremblay, whose findings are reported in the journal Nature Genetics, described the find as "very important and surprising". He said: "The excitement is not because it's another mouse story.

"The excitement is we are not going to have to wait for seven years of research.The compound has already been developed in many cases.

"Clinical trials for diabetes have shown that the drug has very low toxicity in comparison to other anti-cancer treatments, so the side effects are minimal, especially when it's administered for a very short period.

"Today, we are starting to look at the role of PTP1B in other types of cancer, like ovarian cancer and certain deadly kinds of adult leukaemia. We hope to start those studies in the months ahead."

Dr Philip Branton, of the Canadian Institute of Cancer Research, said: "This is already halfway or more than halfway down the pipeline.

"They already have a drug, it's already been looked at in the clinic for safety and so on, so it could potentially by fast-tracked for clinical trials in use in cancer."

The mice involved were genetically engineered to make a rogue protein that fuels the growth of up to a quarter of breast cancers in women.

The best treatment for this type, which grows and spreads particularly quickly - is the drug Herceptin.

Dr Tremblay said that combining the new drugs with Herceptin could provide 'a two-way kill'.