Abiraterone works by blocking production of the hormones throughout the body.
The latest study, published in the Journal of Clinical Oncology, is based on just 21 patients with advanced, aggressive prostate cancer treated with the drug - but data has been collected on a total of 250 worldwide.
It found significant tumour shrinkage, and a drop in tell-tale levels of a key protein produced by the cancer called prostate specific antigen in the majority of patients.
Many of the patients have reported a significant improvement in the quality of their lives.
Some were able to stop taking morphine for the relief of pain caused by the spread of the disease to their bones.
Lead researcher Dr Johann de Bono said the findings needed to be confirmed in larger trials.
We believe we have made a major step forward in the treatment of end-stage prostate cancer patients
Dr Johann de Bono Institute of Cancer Research
At this stage, no patient has taken the drug for longer than two-and-a-half years, and so it has not been possible to determine exactly what the effect of the drug on life expectancy will be.
But he said: "We believe we have made a major step forward in the treatment of end-stage prostate cancer patients.
"These men have very aggressive prostate cancer which is exceptionally difficult to treat and almost always proves to be fatal.
"We hope that abiraterone will eventually offer them real hope of an effective way of managing their condition and prolonging their lives."
It is hoped the drug will also aid other cancer patients, including those with breast cancer.
Professor David Webb, an expert in clinical pharmacology at the University of Edinburgh, said: "This agent clearly looks promising, but it is still at the early stages of clinical development.
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