Validation of a prognostic model for metastatic castrate-resistant prostate cancer (mCRPC) patients receiving abiraterone acetate (AA).

Abstract

5013 Background: A prognostic model based on clinical parameters has been derived from the population of the COU-AA-301 Phase 3 trial for mCRPC patients treated with AA after docetaxel. It relies on the presence of six clinical parameters: ECOG-PS=2, presence of liver metastases, time from start of initial LHRH agonist therapy to AA therapy ≤36mths, low albumin, high alkaline phosphatase and high LDH (1 point per parameter) to stratify patients into 3 risk groups. We sought to validate this model in an independent cohort of patients treated with AA post-docetaxel, and to explore its utility in patients treated with AA in the pre-chemotherapy setting. Methods: We reviewed all mCRPC patients who received AA between January 2006 and June 2013 at our centre who either received AA post-docetaxel outside of a clinical trial (group A, validation set) or were treated with AA prior to chemotherapy (group B, exploratory analysis). Clinical data at the time of starting treatment with AA and outcome was collected from electronic patient records. Patients were assigned into ‘good’ (0-1), ‘intermediate’ (2-3), and ‘poor’ (4-6) prognostic groups as per the published model (Chi KN et al, J Clin Oncol 2013;abstr 5013). Differences in median overall survival (mOS) were assessed using the log-rank test. Results: A total of 158 patients were eligible for this analysis (group A: n=94, group B: n=64). Median duration of AA therapy and mOS were 4.7mths and 13.3mths (group A), and 15.3mths and 40.4mths (group B) respectively. When considering the validation set of patients post-docetaxel, mOS was significantly different across the three prognostic groups (good: n=39, mOS=21.8mths; intermediate: n=44, mOS=10.6mths; poor: n=7, mOS=6.8mths; p=0.0001). Analysis of group B confirmed the ability of the model to prognosticate for OS in the pre-chemotherapy setting: (good: n=44, mOS=45.6mths; intermediate or poor: n=20, mOS=34.5mths; p=0.042). Conclusions: These results serve to validate the prognostic model in an independent, unselected population treated with AA post-docetaxel and support clinical implementation of the score. Additionally, the model remains valid in the pre-chemotherapy setting.