The researchers believe that their breakthrough study will pave the way for drugs which target the mutation and stop the cancer spreading.
"We have identified mutations in a gene that helps to control cell movement. We believe that the cancer cells have hijacked this gene to help them spread," said Dr Magali Williamson, who led the team at the Prostate Cancer Research Centre at University College London.
"We found mutations in nearly half of the cancers restricted to the prostate, and nearly all the ones that have spread, suggesting that the mutations might be helping the cancer cells spread," he added.
During the study, the researchers examined 12 prostate cancer patients whose disease had spread, and found that 90 percent of them had the mutant gene.
They also looked at 100 men whose cancer had not spread, and observed that only 45 percent of them had the mutant gene.
They have also found that men who were overweight when diagnosed with prostate cancer were twice more likely to die from the disease.
Professor John Masters, a specialist at the centre, said: "If we could switch off this gene with drugs we might prevent its spread and save lives."