Abiraterone Improves Survival in Metastatic Prostate Cancer

A multinational phase III trial found that the drug abiraterone acetate prolonged the median survival time of patients with metastatic castration-resistant prostate cancer by 4 months compared with patients who received a placebo. The preliminary results from the study were presented October 11, 2010, at the 35th Congress of the European Society for Medical Oncology (ESMO) in Milan, Italy, and subsequently published in the New England Journal of Medicine on May 26, 2011 (see the abstract).

Standard prostate cancer treatments reduce blood levels of testosterone, the hormone that fuels the cancer’s growth. However, most prostate cancers eventually become resistant to these treatments. Such cancers are called castration-resistant prostate cancers. Abiraterone acetate is designed to treat these tumors by inhibiting the production of androgen in the testes, adrenal glands, and prostate cancer tumors themselves.

The clinical trial included 1,195 patients from 13 countries whose metastatic prostate cancer had previously been treated with one of two chemotherapy regimens that included docetaxel. Among the 797 patients randomly assigned to receive abiraterone acetate plus the corticosteroid prednisone, median overall survival was 14.8 months. Among the 398 who received prednisone plus placebo, median survival was 10.9 months.

Differences between the placebo and treatment groups also emerged for all of the trial’s secondary endpoints, including the time that it took for prostate-specific antigen (PSA) levels to increase, progression-free survival according to medical imaging, and the number of patients who experienced reductions in PSA levels after treatment. The benefits of abiraterone were determined during a prespecified interim analysis of the study results, prompting the trial’s Independent Data Monitoring Committee to recommend unblinding the trial and offering abiraterone acetate to patients in the placebo arm.

“This is a major step forward in prostate cancer therapeutics,” said principal investigator Johann de Bono, M.D., Ph.D., of the Institute of Cancer Research and the Royal Marsden Hospital in the United Kingdom. “Men with metastatic … castration-resistant prostate cancer have a poor prognosis, with only about one in three alive 5 years after diagnosis,” he explained. “For many men, abiraterone acetate can extend life.”

On the basis of these results, the Food and Drug Administration (FDA) approved abiraterone in April 2011 for men with metastatic castration-resistant prostate cancer that has previously been treated with a chemotherapy regimen containing docetaxel. Abiraterone is the second drug approved for this type of advanced prostate cancer since June 2010.

Editor's note: In December 2012, the FDA expanded the approval of abiraterone (in combination with prednisone) to treat men with metastatic castration-resistant prostate cancer who have not previously undergone chemotherapy. Results of the study that led to the expanded approval were published December 10, 2012, in the New England Journal of Medicine.