A drug currently used to treat obesity may also be able to fight prostate cancer, a study suggests.

Scientists in the United States say they have found that Xenical can stop the disease spreading in mice.

Writing for the journal Cancer Research, they described the finding as “a big advance”.

While more research is needed, the study could open the door to trials to see if the drug can fight prostate cancer in humans.

Xenical, which is manufactured by Roche, was launched in the UK six years ago as a treatment for obesity. Studies have shown that it can help people to lose weight.

Over half a million prescriptions for the drug are written by doctors in England every year.

The drug works by blocking the absorption of fat in the gut and is taken as part of a low-fat diet.

Dr Jeffrey Smith and colleagues at The Burnham Institute in California analysed prostate cancer cells in their laboratory.

They found that a protein that enables the body to turn food to fat is also found in prostate cancer cells.

US funding

Laboratory tests showed that by using Xenical to block this protein, they could stop cancer cells from spreading. Tests on mice produced similar results.

The study, which was funded by the US government, also found that the drug did not affect normal prostate cells. It also had no apparent side effects in the mice.

Dr Smith hailed the findings. “This is a big advance in the sense that we have an approved drug - approved for one indication - that has another target and another potential disease indication, prostate cancer.”

The fact that the drug is already approved for use in humans means clinical trials to see if it is effective against prostate cancer could begin much sooner than would otherwise be the case.

Professor Nick James of Cancer Research UK said it was plausible that the drug could help people with prostate cancer.

“Obesity is closely associated with both incidence of prostate cancer and survival from the disease.

“It is perfectly plausible that techniques targeting the way the body processes fat could be effective against prostate cancer.”

A spokeswoman for Roche welcomed the study. “It’s very exciting,” she told BBC News Online.

“There are no current plans to carry out our own research in this area but we will watch how this research progresses.”