Larger trials are needed to further examine and confirm the early findings on the experimental drug abiraterone acetate (CB7630). Researcher Dr. Johann de Bono, from the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust in the UK, who led two ongoing clinical trials of CB7630, said larger studies are necessary to find out the efficacy of the drug. "We believe we have made a major step forward in the treatment of end-stage prostate cancer patients," De Bono told BBC News. He, however, added that the phase 1 and 2 findings needed to be confirmed in larger trials.

An oral and irreversible inhibitor of the enzyme CYP17 that decreases testosterone and DHT to undetectable levels, CB7630 works by blocking the production of the hormones throughout the body. The latest abiraterone study, published in the Journal of Clinical Oncology, is based on just 21 patients with advanced, aggressive prostate cancer treated with the drug although data has been collected on a total of 250 patients in the US and the UK. The studies found significant tumour shrinkage and a drop in PSA in the majority of patients.

In an interview with Urosource, Prof. Fritz Schröder of the Department of Urology, Erasmus MC, University Medical Centre Rotterdam, The Netherlands, called the latest CB7630 findings an "important and exciting development" in ongoing research concerning androgen-independent prostate cancer (AIPC), but reiterated the view that there are still some key questions that require further studies and which can only be answered in larger trials.

In a paper published in the latest issue of European Urology, Schröder said that based on recent findings it is "evident that enzymes related to androgen metabolism that are over-expressed in AIPC could be targets for endocrine treatment." He said CBT7630 is a recent example.

Per-Anders Abrahamsson, Secretary-General of the EAU, said arbiraterone acetate targets a group of patients that are notoriously hard to treat, adding that it would be a breakthrough if abiraterone can fulfil the promises of the initial data. "Caution is indeed in order and it is too early to warrant too much excitement and raise expectations amongst patients just yet," said Abrahamsson.

Professor David Webb, an expert in clinical pharmacology at the University of Edinburgh, also said in a BBC News interview that although abiraterone acetate "clearly looks promising…it is still at the early stages of clinical development." "It will be crucial to look carefully at the balance between its benefits and harms, before drawing firm conclusions about the usefulness of this new drug," said Webb. "Important side effects often only emerge with the larger clinical studies that now need to be done."

Abiraterone, developed by the US-based Cougar Biotechnology (Los Angeles, California), is now being readied for phase 3 trials worldwide.

European Association of Urology