Scientists have for the first time discovered that genetic information taken from molecules found inside bubbles of fat in a man's urine could be a useful new biomarker for showing whether his prostate cancer is aggressive or not.

The study is the work of lead author Dr Jonas Nilsson, who is based at the VU University Medical Centre in Amsterdam, The Netherlands, and is to be published today, 13 May, in the British Journal of Cancer.

Exosomes are tiny capsules of fat that contain genetic material called RNA that comes directly from tumors. The idea is that by looking at the RNA molecules the researchers can tell which genes are turned on and off in that particular person's cancer.

While exomes are found in urine of people with and without cancer, some cancer cells appear to shed a lot more of them.

Until now, the biomarkers used to diagnose prostate cancer have been proteins, for example the PSA test that uses prostate specific antigen.

But Nilsson and colleagues have developed a new way that analyses the genetic instructions themselves, which is what goes wrong when cancer develops.

Different genes are switched on an off in different cancers, and the patterns are also different depending on whether the cancer is aggressive or dormant. By analysing the RNA molecules shed by the cancer cells, Nilsson and colleagues say it should be possible to see which pattern corresponds to aggressive prostate cancer.

This method could be used to develop a diagnostic test that helps doctors decide which prostate cancers are aggressive and need to be treated right away, and which can be left untreated and just monitored incase they need treatment later.

Invasive treatment for prostate cancer carries risk of long term incontinence and impotence, so it is important that this is not done unless absolutely necessary, hence reliability of diagnosis is a vital area of prostate cancer research.

Prostate cancer is the most common cancer in men in the UK, where about 34,000 men are newly diagnosed and 10,000 men die from the disease every year.