DNA testing can predict which men face the highest risk of deadly prostate cancer, scientists say.
The team at the Institute of Cancer Research, in London, say men could soon be offered genetic screening in a similar way to breast cancer in women.
They have shown 14 separate mutations can greatly increase the odds of aggressive prostate cancers, which could form the basis of a test.
Prostate Cancer UK said such testing could "revolutionise" care for men.
Prostate cancer is the commonest cancer in men in many countries, including the UK - where more than 40,000 people are diagnosed each year.
But not every patient has, or needs, invasive therapy that results in severe side-effects.
Identifying which men will need treatment - those who are likely to develop the most aggressive and deadly form of the cancer - is a huge challenge.
Danger genes
The researchers took blood samples from 191 men with prostate cancer and at least three close family members with the same condition.
Each was tested for risky mutations - this included the BRCA genes that are involved in repairing DNA and already linked to breast and ovarian cancers.
The results, published in the British Journal of Cancer, show that 7% of the men had one of 14 high-risk mutations.
The researchers said that it was also these men who had the aggressive prostate cancer that had started to spread around the body.
One of the researchers, Dr Zsofia Kote-Jarai, told the BBC: "I can see in two to three years offering screening to men with prostate cancer and to men worried about their family history."
However, she said it was unlikely these men would immediately opt to have their prostate removed.
Many women with a high risk of breast cancer, for example Hollywood actress Angelina Jolie, opt to have their breast tissue removed.
"A mastectomy is removing an organ we don't really need, and there is excellent plastic surgery afterwards. Radical prostatectomy has really big side-effects. It is more likely men will be monitored more closely."
The side-effects include infertility, difficulty maintaining and keeping an erection, and uncontrolled urination.
'Exciting'
However, the screening is not ready yet. The research group is already running a larger trial involving 2,000 men and testing 192 genes.
Dr Iain Frame, the director of research at the charity Prostate Cancer UK, said: "We urgently need to understand more about which men are at risk of developing prostate cancer, and in particular aggressive forms of the disease.
"Genetic testing to predict risk could revolutionise how we treat the 40,000 men diagnosed with the disease every year in the UK.
"These results are exciting as they add to the growing weight of evidence that men with a family history of prostate cancer who possess certain genes may be at higher risk, providing us with another crucial piece of the jigsaw."
Source: BBC