A drug discovered in the UK could help thousands of men with advanced prostate cancer, experts say.
Trials involving men who had exhausted all other treatment options found abiraterone acetate extended life by an average of four months.
Researchers hope that in less advanced cases, the benefits could be greater.
The drug's makers, the pharmaceutical firm Janssen, are now seeking a licence which would allow it to be used on the NHS.
More than 36,000 men are diagnosed with prostate cancer each year in the UK - more than 10,000 die from the disease.
If the disease spreads beyond the prostate, a small gland found near the bladder, then it becomes far more difficult to treat.
Abiraterone acetate interferes with the production of the hormone testosterone, which can fuel the growth of prostate cancer.
The trials involved more than 1,000 men with very advanced, aggressive cancers, whose prognosis was poor, with only months left to live.
The 797 patients given abiraterone plus a steroid lived for an average of 14.8 months, compared to 10.9 months for the remainder who simply got the steroid.
Scans showed that tumour growth halted for longer in the group given the drug.
Another advantage of the drug was the relative lack of side effects compared with chemotherapy or radiotherapy, making it a far more attractive prospect for patients.
The drug was first discovered at the Institute of Cancer Research in London, and its chief executive Professor Peter Rigby said he was "very proud" that men with advanced prostate cancer had this new treatment option.
Other cancer charities, who helped fund research into the drug, also welcomed the study results, presented at the European cancer drug conference ESMO.
John Neate, from the Prostate Cancer Charity, said that the drug represented a "significant move forward".
He said: "These initial findings are particularly important as they offer new hope to men diagnosed with an advanced form of prostate cancer who can quickly run out of treatment options once their tumour stops responding to the existing methods of controlling its progression."
He said that while the full results of the study had yet to be published in medical journals, he hoped that they would provide the evidence needed to allow the drug to be licensed for use in the NHS.
Harpal Kumar from Cancer Research UK, added: "It's certainly a significant improvement in what might be expected for men with such advanced prostate cancer."
Pharmaceutical firm Janssen will now apply for a European licence, which would allow UK doctors to prescribe it, although there is no decision yet on how much it should cost.
Further trials will look at whether men with slightly less advanced prostate cancer could also benefit from the drug, perhaps even more than those taking part in this study.