Cougar Biotechnology Initiates Phase II Trial of CB7630 (Abiraterone Acetate).

LOS ANGELES -- Cougar Biotechnology, Inc., a publicly held biotechnology company, today announced that it has initiated a Phase II trial of its drug candidate CB7630 (abiraterone acetate), an orally active inhibitor of the steroidal enzyme 17alpha-hydroxylase/C17,20 lyase, for the treatment of advanced prostate cancer. The Phase II trial is being conducted at The Institute of Cancer Research, in the Cancer Research UK Centre for Cancer Therapeutics, and at The Royal Marsden NHS Foundation Trust in the United Kingdom.

The Phase II study will evaluate the efficacy of CB7630 administered daily to patients with chemotherapy-naE[macron]ve hormone refractory prostate cancer (HRPC) with a rising PSA (prostate specific antigen) despite hormonal therapy. Efficacy evaluations in the trial will include declines in PSA levels, tumor shrinkage (as measured using the RECIST criteria), duration of response (by PSA and RECIST criteria) and time to disease progression. Cougar expects a total of 35 patients will be enrolled in the trial. Results from the Phase I trial of CB7630, conducted at The Institute of Cancer Research and at The Royal Marsden NHS Foundation Trust and presented at the recent American Association for Cancer Research Innovations in Prostate Cancer Research Conference, indicated that abiraterone was safe and well-tolerated. The results also showed that CB7630 was associated with decreases in PSA levels, tumor shrinkage (as evaluated by RECIST criteria), radiographic regression of bone metastases and improvement in pain.

Dr. Johann S. deBono, MSc, PhD, MD, FRCP, the principal investigator of the trial, said, "We are pleased to be able to begin this Phase II trial. The recently presented Phase I trial results of CB7630 demonstrated an intriguing initial indication of the efficacy of the drug in patients with hormone refractory prostate cancer. We greatly look forward to rapidly enrolling this Phase II trial and further investigating the efficacy of this novel, targeted therapy."

Dr. Arie Belldegrun, MD, FACS, Vice Chairman of the Board of Directors of Cougar Biotechnology, said, "The activity of CB7630 observed in the Phase I trial suggests that CB7630 could represent an important second line therapy for patients with advanced prostate cancer who fail first-line hormonal treatment. Despite the approval of several new cancer drugs in recent years, there continues to be a need for new treatments for HRPC." Alan H. Auerbach, Chief Executive Officer and President of Cougar Biotechnology, added, "We are pleased to be able to advance CB7630 into a Phase II trial approximately one year after initiating the Phase I trial of the drug. We continue to look forward to further progressing the clinical development of CB7630 in advanced prostate cancer."

About Cougar Biotechnology

Cougar Biotechnology, Inc. is a Los Angeles-based publicly held biotechnology company established to in-license and develop clinical stage drugs, with a specific focus on the field of oncology. Cougar's oncology portfolio includes CB7630, a targeted inhibitor of the 17alpha-hydroxylase/C17,20 lyase enzyme which is currently being tested in a Phase II clinical trial in prostate cancer; CB3304, an inhibitor of microtubule dynamics which is currently in a Phase I trial in hematological malignancies and CB1089, an analog of vitamin D which has been clinically tested in a number of solid tumor types.

Further information about Cougar Biotechnology can be found at www.cougarbiotechnology.com.

This press release contains forward-looking statements that involve risks and uncertainties that could cause Cougar's actual results and experiences to differ materially from the anticipated results and expectations expressed in these forward-looking statements. These statements are often, but not always, made through the use of words or phrases such as "anticipates," "expects," "plans," "believes," "intends," and similar words or phrases. These statements are based on current expectations, forecasts and assumptions that are subject to risks and uncertainties, which could cause actual outcomes and results to differ materially from these statements. Among other things, there can be no assurances that the development of CB7630 will ever be successfully completed, that Cougar will ever receive the regulatory approvals necessary to commercialize CB7630, or that Phase II trials of CB7630 will be successful. Other risks that may affect forward-looking information contained in this press release include the risk that the results of clinical trials may not support Cougar's claims, Cougar's reliance on third-party researchers to develop its product candidates, and its lack of experience in developing and commercializing pharmaceutical products. Additional risks are described in the company's Current Report on Form 8-K filed with the Securities and Exchange Commission on April 7, 2006. Cougar assumes no obligation to update these statements, except as required by law.