Results observed from pre-specified interim analyses of the randomized, placebo-controlled Phase 3 study, COU-AA-302, demonstrated that patients with metastatic castration-resistant prostate cancer (mCRPC) treated with abiraterone acetate (ZYTIGA®) plus prednisone showed a statistically significant improvement in radiographic progression-free survival (rPFS) and all secondary endpoints compared to patients treated with placebo plus prednisone. The results, announced today by Janssen Research & Development, LLC, also showed a trend for increased median overall survival (OS), the co-primary endpoint, in patients receiving ZYTIGA plus prednisone. The study included 1,088 asymptomatic or mildly symptomatic patients with mCRPC who had not received chemotherapy.
This is the first randomized study to demonstrate a radiographic progression-free survival benefit and an overall survival trend in this patient population. The COU-AA-302 results are being presented at the 48th Annual Meeting of the American Society of Clinical Oncology (ASCO).
"These results are very promising for abiraterone acetate in the treatment of patients with metastatic castration-resistant prostate cancer who are asymptomatic or mildly symptomatic and have not received chemotherapy. The results also advance our understanding of the role of androgen biosynthesis inhibition in this patient population," said Charles J. Ryan, M.D., lead investigator of the study and Associate Professor of Clinical Medicine at the UCSF Helen Diller Family Comprehensive Cancer Center. "This is an important study with all clinically relevant endpoints favoring treatment with abiraterone acetate plus prednisone, and is also the first to suggest that inhibiting androgen production significantly delays initiation of cytotoxic chemotherapy."
The data demonstrate a statistically significant improvement in rPFS in the abiraterone acetate plus prednisone arm (ZYTIGA arm) of the study compared to the placebo plus prednisone (control) arm. The median rPFS in the control arm was 8.3 months but had not yet been reached in the ZYTIGA arm because progression events were occurring more slowly in the ZYTIGA arm compared to the control arm (N=150 vs. 251, respectively). The Hazard Ratio (HR) equaled 0.43, there was a 95% confidence interval (CI): [0.35, 0.52], and the p-value was <0.0001.
Additionally, treatment with ZYTIGA plus prednisone resulted in an estimated 33 percent improvement in survival (median overall survival in the ZYTIGA arm was not reached and was 27.2 months in the control arm; HR=0.75; 95% CI: [0.61, 0.93], p=0.0097). At the time of these interim analyses, the pre-specified p-value of 0.0008 to achieve statistical significance was not reached.
Secondary Endpoints
Treatment with ZYTIGA plus prednisone also suggested significant improvements in secondary study endpoints compared to the control arm, specifically, longer time until: