Does Gleason score (GS) predict efficacy of abiraterone acetate (AA) therapy in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)? An analysis of AA phase 3 trials.

Abstract

20 Background: GS is strongly prognostic in localized PC but is less so in mCRPC (Halabi S, J Clin Oncol 2003; Armstrong AJ, Eur J Cancer 2010). Pts with high-risk localized PC and high GS who undergo radiation therapy benefit from long-term androgen deprivation therapy (Horwitz EM, J Clin Oncol 2008). In mCRPC, the impact of GS at initial diagnosis on response to AA therapy is unknown. We retrospectively evaluated efficacy outcomes in pts with mCRPC treated with AA plus prednisone (P) vs P alone in pivotal studies COU-AA-301 (post-docetaxel) and COU-AA-302 (chemo-naive) by GS (≥ 8 or < 8). Methods: 1,048 pts in COU-AA-301 and 996 in COU-AA-302 with mCRPC treated with AA 1 g + P 5 mg po BID or placebo + P had GS data at diagnosis. Efficacy end points evaluated: overall survival (OS), radiographic progression free survival (rPFS), and time to prostate-specific antigen progression (TTPP) (de Bono JS, NEJM 2011; Fizazi K, Lancet Oncol 2012; Ryan CR, NEJM 2013). Distributions and medians were estimated by the Kaplan-Meier method, and hazard ratio (HR) and 95% confidence interval were estimated by the Cox model. Results: Proportion of pts with GS ≥ 8 and GS < 8 was similar across treatment groups and studies. Outcomes by GS are summarized in the Table. Conclusions: GS (≥ 8 or < 8) at initial diagnosis was not predictive of treatment benefit of AA + P vs P alone in post-docetaxel and chemo-naïve pts with mCRPC, with both groups benefiting. In this era of novel androgen signaling targeted agents, GS may not be relevant in predicting efficacy with AA for pts with mCRPC. Clinical trial information: NCT00638690, NCT00887198. [Table: see text]