An early-stage trial of Cougar Biotechnology's oral treatment abiraterone has generated huge excitement after it demonstrated significant anti-tumour activity in men with chemotherapy-resistant prostate cancer.

Data from the Phase I trial, which have been published in the Journal of Clinical Oncology show that 21 chemotherapy-naive men with prostate cancer resistant to multiple hormonal therapies experienced significant tumour shrinkage and reduction in prostate-specific antigen (PSA) levels when treated with abiraterone, also known as CB7630.

70%-80% of the patients saw a reduction in PSA levels and the data also demonstrated that abiraterone delayed disease progression by a median of 400 days. The trial was conducted by the Institute of Cancer Research and the Royal Marsden Hospital in the UK and the researchers noted that this is the first study to demonstrate that the continuous inhibition of the CYP17 enzyme is safe and has measurable effects on tumours.

Lead researcher Johann de Bono said that the Royal Marsden patients in the study have been monitored for up to two-and-a-half years and with continued use of abiraterone they were able to control their disease with few side-effects. A number of patients were able to stop taking morphine for the relief of bone pain.

"These men have very aggressive prostate cancer which is exceptionally difficult to treat and almost always proves to be fatal”, he noted and while he cautioned about jumping to too many conclusions on such a small study, “we hope that abiraterone will eventually offer them real hope of an effective way of managing their condition and prolonging their lives”.

The researchers have recommended that further studies should use a dose of 1000mg daily and earlier this year, Cougar commenced a 1,200-patient Phase III trial in men with metastatic castration-resistant prostate cancer who have failed standard chemotherapy.

John Neate, chief executive of The UK’s Prostate Cancer Charity said “this is an exciting development which has been eagerly anticipated”. He noted that advanced prostate cancer is very difficult to treat as, after a period of time, it stops responding to conventional ways of controlling testosterone, essential to the cancer’s continued growth.

Mr Neate concluded by saying that “we look forward to the results of the larger trials already underway or being planned for this drug to prove its potential effectiveness for the thousands of men diagnosed with advanced prostate cancer every year”.