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Being overweight or obese may increase a man's risk of aggressive prostate cancer, researchers believe after doing animal and human cell studies.

The French investigators found that fat cells release a protein that drives prostate cancer's spread in mice.

Human fat cells release the same protein, they told .

The researchers hope that drugs which block it could help treat men before the disease becomes too advanced.

Drugs that do this are already being tested in human trials for another, unrelated health condition - asthma.

In the UK, about one in eight men will get prostate cancer at some point in their lives.

Diagnosed early, the chances of survival are generally good. But prostate cancer kills more than 10,000 men a year in Britain.

Obesity and cancer

Many cancers are linked to being overweight.

These include breast, bowel and womb cancer.

But any link with prostate cancer has been less clear.

Lead researcher Dr Catherine Muller, from Toulouse University, says while obesity may not make prostate cancer more likely, it does appear to fuel its growth if a tumour is already present.

"This is something people need to know. People are aware about obesity's importance in other cancers and diseases, but not for prostate cancer."

Her lab work shows how the protein CCL7 from fat cells signals for cancer cells to move out of the prostate gland and into the surrounding tissue.

In obese mice who had been fed a high-fat diet, tumour spread outside the prostate was greater than in mice with normal body weight and was linked to higher levels of CCL7 and its target receptor CCR3.

They then studied more than 100 human tumour samples and confirmed that the aggressive cancers tended to have more CCR3 receptors than less aggressive ones.

Dr Aine McCarthy, Cancer Research UK's science information officer, said: "This research in mice sheds light on why obese men with prostate cancer are more likely to have aggressive tumours. It shows for the first time how fat cells surrounding the prostate use chemical signals to talk to tumour cells, enticing them to move and spread around the body.

"Excitingly, the researchers proved that jamming communications between fat cells and tumour cells stopped the cancer spreading. The next step is to assess if this approach, using drugs that are already being developed, could benefit men with the disease."