It can identify patients with a 10 times higher risk of dying from the disease.
The results allow doctors to boost survival chances by giving targeted treatments more quickly. The test looks for rare free-ranging tumor cells that spread the disease around the body.
Around 11,000 die from the disease, which is often localized, slow-growing, and relatively simple to treat.
In other cases it is more aggressive and likely to spread to other parts of the body.
But researchers can now predict if it will spread with 92 percent accuracy after analyzing blood samples from 81 prostate cancer patients.
The researchers, who published their findings in journal Clinical Cancer Research, are working to see if the test can be used on other types of cancer.
Rebecca Porta, from male cancer charity Orchid, said: “Delivering more appropriate treatment more quickly could help save lives and prolong life expectancy.”