Abstract
14 Background: Abiraterone acetate (AA), a prodrug of abiraterone, which is a selective androgen biosynthesis inhibitor, prolongs overall survival (OS) in mCRPC pts and is approved for use in this population. An exploratory analysis was conducted to determine the impact of prior endocrine therapy on clinical benefit of AA in COU-AA-302, a randomized phase 3 study of pts with chemotherapy-naive mCRPC. Methods: 1,088 pts (testosterone < 50 ng/dL; receiving continuous gonadotropin-releasing hormone [GnRH] agonist if not orchiectomized) were randomized 1:1 to AA (1 g) + prednisone (P) (5 mg BID) or placebo + P alone. rPFS and OS were co-primary end points. rPFS was defined as time to first occurrence of bone scan progression by PCWG2 criteria, progression by CT/MRI by modified RECIST 1.0 criteria, or death, whichever came first. Comparison of the treatment effect on rPFS (investigator review at 55% of OS events) was made for the subgroups above or below the median duration of prior endocrine therapy in 2 categories: either prior GnRH agonist or prior antiandrogens. Cox model was used to obtain the HR and associated 95% CI with statistical inference by log rank statistic. Results: Most pts received prior GnRH agonists and antiandrogens (Table). rPFS was significantly more favorable with AA than P irrespective of the median duration of prior GnRH agonist or antiandrogen therapy. Increased median rPFS was observed in pts with longer prior exposure to GnRH agonists or antiandrogens comparing within both AA and P treatment groups. Conclusions: As shown in this COU-AA-302 exploratory analysis, duration of prior endocrine therapy, as analyzed after the onset of mCRPC, does not appear to impact clinical benefit of AA in pts with chemotherapy-naive mCRPC. Clinical trial information: NCT00887198. [Table: see text]
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