ORLANDO, FL USA (UroToday.com) - Dr. Fred Saad presented a multi-institutional, exploratory analysis to evaluate the effect of prior endocrine therapy on clinical benefit of abiraterone (AA) in chemotherapy-naïve patients with metastatic castration-resistant prostate cancer (mCRPC) in the randomized phase III study, COU-AA-302. A total of 1 088 patients who received continuous gonadotropin-releasing hormone [GnRH] agonists were randomized 1:1 to AA (1 g) + prednisone (P) (5 mg BID) or placebo + P. Radiographic progression-free survival (rPFS) and OS were “co-primary” end points of this trial. The rPFS was defined as time to first occurrence of bone scan, CT, or MRI progression, or death, whichever came first. They compared the treatment effect of AA on rPFS (investigator review at 55% of OS events) for subgroups above or below the median duration of prior endocrine therapy in 2 categories: prior GnRH agonists and androgen receptor (AR) inhibitors. Cox model was used to obtain the hazard ratio (HR) and associated 95% confidence interval (CI) with statistical inference by log rank statistic.
According to Dr. Saad, irrespective of median duration of prior GnRH agonist or AR inhibitor therapy, rPFS was significantly more favorable with AA + P than placebo + P. Moreover, increased median rPFS was evident in patients who had longer prior exposure to GnRH agonists or AR inhibitors, as compared to both AA + P and placebo + P treatment groups.
Abiraterone is a specific CYP17 inhibitor, and with prednisone, randomized clinical trials have shown that it can have significant improvement in rPFS in chemotherapy-naïve, asymptomatic or mildly symptomatic men who have progressive mCRPC. In this exploratory analysis, clinical benefit with AA + P vs placebo + P was demonstrated by significantly improved rPFS, regardless of whether men had exposure to prior endocrine therapy above or below the median duration of 37 and 16 months for GnRH agonists or AR inhibitors, respectively. Prior GnRH agonist and anti-androgen treatment duration should be further studied in order to fully assess their impact.
Click HERE to view the poster from this session
Presented by Fred Saad, MD, FRCSC at the American Urological Association (AUA) Annual Meeting- May 16 - 21, 2014 - Orlando, Florida USA
University of Montreal Hospital Centers, Montreal, Quebec Canada
Written by Reza Mehrazin, MD, medical writer for UroToday.com