Men with prostate cancer and an inherited gene mutation have the worst form of the disease, research reveals.
The BRCA2 gene is linked to hereditary breast cancer, as well as prostate and ovarian cancer.
Now scientists say that as well as being more likely to get prostate cancer, men with BRCA2 are also more likely to develop aggressive tumours and have the poorest survival rates.
They say these men should be treated quickly to save lives.
Around one in every 100 men with prostate cancer will have the BRCA2 mutation.
These men might benefit from immediate surgery or radiotherapy, even if their disease is at an early stage and would normally be classified as low risk, according to the latest work in the Journal of Clinical Oncology.
Prostate cancer can grow extremely slowly or very quickly, and this is something that is hard to predict early on.
Some men may live symptom-free for a lifetime, despite having this cancer.
For many, treatment is not immediately necessary.
But researchers say men with BRCA2 and prostate cancer should be treated early and aggressively because their tumour is more likely to spread.
Prof Ros Eeles and colleagues at The Institute of Cancer Research in London and The Royal Marsden NHS Foundation Trust found prostate cancers spread more quickly and were more often fatal in men who had inherited a faulty BRCA2 gene than in men without the faulty gene.
They looked at the medical records of prostate cancer patients which included 61 men with BRCA2, 18 men with a similar gene mutation called BRCA1, and 1,940 men with neither mutations.
Patients with BRCA2-mutations were significantly less likely to survive their cancer, living an average of 6.5 years after diagnosis compared with 12.9 years for non-carriers. They were also more likely to have advanced disease at the time of diagnosis.
'More deadly type'
Prof Eeles said: "It is clear from our study that prostate cancers linked to inheritance of the BRCA2 cancer gene are more deadly than other types.
"It must make sense to start offering affected men immediate surgery or radiotherapy, even for early-stage cases that would otherwise be classified as low-risk.
"We won't be able to tell for certain that earlier treatment can benefit men with inherited cancer genes until we've tested it in a clinical trial, but the hope is that our study will ultimately save lives by directing treatment at those who most need it."
More than 40,000 men are diagnosed with prostate cancer every year.
Men with a significant family history of breast and/or ovarian cancer in addition to prostate cancer can be offered BRCA1/2 testing at diagnosis, but it is not routinely offered to all patients diagnosed with prostate cancer in the UK.
Dr Julie Sharp of Cancer Research UK, said: "This study shows that doctors need to consider treating men with prostate cancer and a faulty BRCA2 gene much sooner than they currently do, rather than waiting to see how the disease develops.
"We knew that men who inherit a faulty BRCA2 gene are at a greater risk of developing prostate cancer but this is the largest study to show that the faulty gene also makes the disease more likely to develop quickly and spread."