Obese men diagnosed with prostate cancer may boost their chances of survival by losing weight, say experts.
Obese men with the disease are advised to lose weight
It follows two studies in the United States which found the disease hits obese men much harder than others.
The studies involving more than 4,000 men found obese men suffered more aggressive forms of the disease and were more likely to suffer a relapse.
Writing in the Journal of Clinical Oncology, the researchers urged obese men with the disease to lose weight.
In the first study, Dr Christopher Amling, who is based at the US Naval Medical Center in San Diego, examined data on 3,162 men with prostate cancer. Of these, 19% were obese.
They found that obese men - with a body mass index score of 30 or more - had more aggressive forms of prostate cancer and a higher rate of recurrence.
In the second study, Dr Stephen Freedland, who is based at the Johns Hopkins University School of Medicine, examined data from 1,106 men with the disease. Some 22% of these were obese.
He found that men who were moderately or severely obese - with a body mass index of 35 or more - had more aggressive forms of the disease.
They were also 60% more likely to have a recurrence of cancer compared with other men.
Both doctors believe that the proteins and hormones in body fat may promote tumour growth in obese men.
These men also have lower levels of testosterone and higher oestrogen levels, which they said may also help fuel the disease.
"The primary role of obesity in prostate cancer is still unclear but it appears to induce the development of more aggressive tumours," said Dr Amling.
"I would advise patients to maintain a normal body weight to limit the possibility that they would develop clinically significant, more aggressive prostate tumours."
In an accompanying editorial in the journal, Professor Alfred Neugut of Columbia University, welcomed the findings.
He said that while further research was needed, the studies could help to cut deaths from prostate cancer.
"Identifying obesity as a risk factor for aggressive prostate cancer is important since it may be one of the few modifiable risk factors for prostate cancer," he said.