Exploratory analysis of survival benefit and prior docetaxel (D) treatment in COU-AA-301, a phase III study of abiraterone acetate (AA) plus prednisone (P) in metastatic castration-resistant prostate cancer (mCRPC).
4558 Background: AA, a selective androgen biosynthesis inhibitor, blocks the action of CYP17, thereby inhibiting adrenal and intratumoral androgen production. AA has demonstrated improved overall survival (OS) by 4.6 months (mos) vs placebo (HR=0.74) in patients (pts) previously treated with D. Methods: COU-AA-301 is a randomized double blind study of AA (1 g) + P (5 mg po BID) vs placebo + P administered to mCRPC pts post-D with a primary endpoint of OS. To further evaluate primary survival result robustness, we performed post hoc exploratory analyses to assess whether the timing of first and last dose of D and reason for D discontinuation impacted OS. Results: At randomization, treatment arms were balanced with respect to baseline characteristics, prior D use, and reasons for discontinuation. In both arms, almost half (45%) discontinued D due to progressive disease (PD); remainder discontinued D after completing all planned cycles (37%), due to toxicity (12%), or for other reasons (5%) per investigator. Median OS from first and last dose of D were longer with AA vs placebo (Table). Median OS was longer with AA vs placebo in pts who discontinued D for PD, or for all other reasons. Conclusions: These exploratory analyses suggest that the OS benefit of AA in mCRPC was maintained when calculated from first or last dose of prior D, and whether or not pts discontinued D for PD. Pts in AA arm of this study had a prolonged median OS of > 32 mos from time of initial D therapy. Congruity among these analyses and lack of dependence on D timing demonstrate robustness of the primary survival result. [Table: see text]