Cougar's prostate drug sees 70 pct response in trials

* Up to 70 pct of men in Phase I/II responded to abiraterone

* BTG set to earn royalties from the drug

* Seen as a major development for prostate cancer

By Ben Deighton

LONDON, May 26 (Reuters) - Cougar Biotechnology's (CGRB.O) prostate cancer drug abiraterone has produced "significant benefits" in about two thirds of men, the results of phase I/II trials have shown.

The Los Angeles-based cancer specialist has released its first full peer-reviewed phase II results, which, in combination with previously released phase I data, show that up to 70 percent of men responded to the drug.

The data, published on Tuesday in the online version of the Journal of Clinical Oncology, show that about two-thirds of men experienced "significant benefits" for an average of eight months, with scans showing their tumours decreased in size.

Johann de Bono, chief investigator of the study, which was undertaken by the British Institute of Cancer Research and the Royal Marsden Hospital, called the results "brilliant".

"The patients involved in this trial remained pain-free for an average of about eight months, a brilliant result for those with aggressive prostate cancer and their families.

"For about a third of men -- those who carried the ERG gene -- the benefit lasted for more than 18 months."

The drug was licensed from British biotechnology company BTG (BGC.L) in April 2004.

Analysts at Piper Jaffray estimate $1 billion sales in 2015 and net 3 percent royalty to BTG.

Last week, U.S. company Johnson & Johnson (JNJ.N) announced that it has agreed to acquire Cougar for about $970 million in cash in order to strengthen its oncology business. [ID:nN21310649] (Editing by Rupert Winchester)