The test, developed by US researchers, involves counting circulating tumour cells (CTCs) in the blood. It is hoped that the test could help tailor treatment for men with advanced prostate cancer and may provide a new way of diagnosing the disease, which accounts for 10,000 deaths in Britain each year.
Current NICE guidance recommends testing PSA levels every three months to see how prostate cancer is progressing in men diagnosed with early localised prostate cancer.
What is the research?
The findings are based on a study of 164 men with prostate cancer who were embarking on first-line chemotherapy treatments.
Measurements of CTC and PSA were taken from blood samples before and after chemotherapy. High values of CTC and PSA before treatment are associated with an increased risk of death.
However, when they took blood samples at four, eight and 12 weeks after chemotherapy, researchers found that increases in CTC counts were associated strongly with risk of death, but changes in PSA were not.
A total of 103 men died from prostate cancer during the 22-month follow-up period. Patients with a high CTC count were 1.58 times more likely to die from prostate cancer than patients with a low CTC count.
Patients with a high PSA level were only 1.26 times more likely to die of the cancer.
What do the researchers say?
Lead researcher Professor Howard Scher, from the Memorial Sloan Kettering Cancer Centre in New York, said: 'CTC number can be used to monitor disease status and might be useful as an intermediate endpoint of survival in clinical trials.'
But he warned that although the data showed that CTCs are a more robust measure of prostate cancer progression than PSA, several prospective trials are needed to generate evidence to guide its use as a biomarker.
What do other researchers say?
John Neate, chief executive of The Prostate Cancer Charity, said: 'Progress is not easy to track with current tests. They work reasonably well but something better is needed.
'Measuring CTCs seems to be more finely attuned to the effects of the chemotherapy than thought previously. There are, therefore, circumstances where some men will benefit from further courses of chemotherapy treatment when at present they may not be offered it.'
Hazel Nunn, health information manager, Cancer Research UK added: 'It can be difficult to work out how well patients are responding to treatment for advanced prostate cancer so this could potentially be of great value to doctors and patients.'
She added: 'We will need large trials to confirm whether this marker could be used to accurately predict a patient's chances of survival.'