Prostate cancer cells under the microscope
If it works, the technique could help spare thousands of older men the risks involved with surgery.
The prostate gland is found near the bladder in men, and its cancer is the second most common male cancer in the UK.
Doctors who discover evidence of prostate cancer face a dilemma, as there is a real risk that intervening could cause more harm than it prevents.
Many prostate cancers are relatively benign and slow-growing, meaning that, particularly in elderly men, they may have no impact on life expectancy.
Risky operation
Surgery to tackle prostate cancer carries a significant risk of incontinence, impotence, or both, as the gland lies close to nerves important to urination and sexual function.
However, others are aggressive and fast-growing, so doctors have to take action with either surgery or radiotherapy.
The latest research, published in the journal Nature on Thursday, looked at prostate samples from 50 men.
Malignant tumours had large numbers of genes which varied from normal prostate tissue, they found.
Researchers then compared tissue from localised, non-spreading prostate tumours, and tissue from aggressive, spreading cancers.
They found two new genes which appear to have a role in the development of the cancer - higher levels of gene expression in the tissue were associated with a worse prognosis for the patient.
Spotting the difference
Professor Mark Rubin, from the University of Michigan Medical School, said: "The ultimate goal is to help physicians determine which patients need to immediate, aggressive treatment and which can be watched and treated conservatively.
"This approach could give us many new diagnostic tests within three to five years.
"Eventually, it could lead to a diagnostic kit physicians could use to determine the best treatment and prognosis for their patients with prostate cancer."
A spokesman for the Cancer Research Campaign said: "Molecular signatures have the power to reveal exactly which genes are switched on and which are switched off in a cancer.
"We already know about some of the key cancer genes. Molecular profiling is throwing up new genes and understanding their function is the next step.
"The short term benefits locked up in genetic signatures lie in diagnosis - molecular profiles give much more specific information on the stage of a tumour than can be gained using conventional diagnostic techniques.
"And this means doctors can better tailor treatment to individual patients. In the long term, genetic signatures are also throwing up new leads for anticancer drug design."