A final analysis of a phase III trial showed that Zytiga (abiraterone acetate) plus prednisone significantly prolonged overall survival compared to an active control of placebo plus prednisone, in men with chemotherapy-naïve metastatic castration-resistant prostate cancer.
The study demonstrated a 19 percent reduction in risk of death in this study population, with a median OS of 34.7 compared to 30.3 months respectively (HR= 0.81 [95% CI, 0.70-0.93]; p = 0.0033), after a median follow-up of more than four years (49.2 months).
“OS is particularly noteworthy in [the study], because 67 percent of men in the Zytiga plus prednisone arm and 80 percent in the control arm received subsequent therapy,” said Charles Ryan, professor of clinical medicine and urology at the University of California, San Francisco, and lead investigator of the study, COU-AA-302. “This includes 44 percent of men in the control arm who subsequently received Zytiga plus prednisone. The use of subsequent therapies did not impact the statistical significance between the Zytiga and control arms, and makes these results all the more compelling after adjusting for the crossover effect.”
In addition, the final analysis demonstrated a significant improvement in median time to opiate use for cancer-related pain compared to placebo plus prednisone, a median 33.4 months vs. 23.4 months respectively (HR= 0.72 [95% CI, 0.61-0.85]; p = 0.0001).
COU-AA-302 is an international, randomized, double-blind, placebo controlled study that included 1,088 men with mCRPC who had not received prior chemotherapy, and were randomized to receive 1,000 mg of Zytiga (abiraterone acetate) administered orally once daily plus prednisone 5 mg administered twice daily, or placebo plus prednisone 5 mg administered twice daily.
FDA, Health Canada, and the European Medicines Agency based approvals of Zytiga plus prednisone for treating men with mCRPC prior to chemotherapy on pre-specified interim analyses of COU-AA-302, which met the co-primary endpoint of radiographic progression-free survival. Based on results from the final analysis, Janssen Research & Development LLC, the drug’s sponsor, has initiated regulatory submissions to relevant health authorities for a revision to the Zytiga label.
