Separating the tigers from the pussycats

Rates of prostate cancer are going up rapidly in Europe and the US. But this isn't necessarily because more people are getting the disease, but because we're diagnosing it more often. In fact, a  large percentage of men in their 80s have prostate cancer, but usually, that isn't the thing that kills them.  And many more men are having a PSA test, which can indicate that they my have cancer.  But often, these cancers are slow growing, and can be safely left or monitored, and will never cause a man significant health problems.

The dilemma of how to tell these harmless 'pussycats' from aggressive and dangerous 'tigers' is something that has puzzled researchers for several years. And it's very important, because treatment for prostate cancer can cause impotence and incontinence, so you really only want to be treating the people who have aggressive tumours.

Now researchers from the University of Michigan have discovered a panel of little chemicals which could lead to a  simple test that could tell doctors whether a man's prostate tumour is a tiger or  pussycat.

Writing in the journal Nature, the scientists, led by Arul Chinnaiyan, looked at over a thousand chemicals in 262 samples of tissue, blood and urine. These chemicals are metabolites - the products of the chemicals reactions that keep us alive, provide us with energy, and help our cells to function normally.

The team compared the metabolite profiles from tissue, blood and urine samples from men with non-cancerous prostates, early stage cancer, advanced prostate cancer and aggressive, spreading cancer.

The researchers found about ten metabolites that were present more often in the cancer samples, and especially in the samples from people with advanced cancer. In particular, they found that the chemical sarcosine was one of the best indicators of advanced prostate cancer - they found high levels in around eight out of ten samples from aggressive cancer, and around four out of ten early cancer samples. But it wasn't found at all in non-cancerous samples. 

Although this is only a small study, the initial results suggest that it could be a better marker of advanced cancer than PSA. And it can also be picked up in urine, which would be a handy fluid for testing.

The researchers also found that sarcosine is involved in the biological pathways that control cancer invasion and spreading. So targeting the production of sarcosine might be a good way to target cancer.

These are still early results, so we won't see a test in clinical use in the immediate future. But once the findings are validated in larger samples of patients in clinical trials, which could take a few years, then we could see it in use in clinics here.