Abiraterone Acetate Improves Overall Survival in Patients with Metastatic Castration-Resistant Prostate Cancer

In a study comprising men with advanced metastatic castration-resistant prostate cancer (CRPC), those who were treated with abiraterone acetate plus prednisone/prednisolone had significant improvement in overall survival (OS) compared with men treated with placebo plus prednisone/prednisolone, according to results published today in the New England Journal of Medicine.

Abiraterone acetate, which was approved by the FDA on April 28, is a biosynthesis inhibitor of androgens, the hormones that promote and maintain male sex characteristics. Androgens can also cause prostate cancer tumors to grow. Abiraterone acetate selectively inhibits the CYP17 enzyme complex, which is needed to produce androgens.

Cougar Biotechnology’s Ortho Biotech Oncology Research & Development unit, an affiliate of Janssen Pharmaceuticals, sponsored COU-AA-301, a randomized, double-blind, placebo-controlled phase III study that was conducted in 147 centers in 13 countries. The trial comprised 1195 men with metastatic advanced CRPC who had been previously treated with docetaxel. Of those patients, 797 men were assigned to receive abiraterone acetate 1000 mg once per day plus prednisone/prednisolone 5 mg twice per day. The other 398 men were assigned to prednisone/prednisolone plus placebo. OS was the primary endpoint.

Johann de Bono,

MD, FRCP, MSc, PhD

After a median follow-up of 12.8 months, the OS for the men in the abiraterone acetate group was 14.8 months; for those in the placebo group, the OS was 10.9 months. According to the study results, compared with those treated with placebo, the men treated with abiraterone acetate also had a 35% reduction in the risk of death (hazard ratio [HR] = 0.646; 95% confidence interval [CI], 0.543-0.768; P <.0001).

The results showed that compared with the men in the placebo group, those in the abiraterone acetate group also had significant improvements in secondary endpoints. Time to PSA progression was 10.2 months for those in the abiraterone group compared with 6.6 months for those in the placebo group (HR = 0.580; 95% CI, 0.462-0.728; P <.0001). The abiraterone acetate group had an increase in radiographic progression-free survival (rPFS) of 5.6 months compared with 3.6 months in the placebo group (HR = 0.673; 95% CI, 0.585-0.776; P <.0001). The total confirmed PSA response (ie, ≥50% decrease from baseline) was achieved in 29% of men in the abiraterone acetate group compared to 6% in the placebo group.

Referring to the study, lead author Johann de Bono, MD, FRCP, MSc, PhD, of the Institute for Cancer Research in London, England, told OncLive.com, “These results are highly significant not only for treating advanced prostate cancer but also for providing insight into the biology of this common male cancer.”