Prognostic Score and Benefit from Abiraterone in First-line Metastatic, Castration-resistant Prostate Cancer

Abstract

Background: Most available prognostic nomograms in metastatic castration-resistant prostate cancer (mCRPC) are derived from datasets not representative of the current treatment landscape. A prognostic nomogram for first-line mCRPC treatment was developed from patients treated in the PREVAIL study.

Objective: To validate the Armstrong model in the COU-AA-302 trial.

Design, setting, and participants: A post hoc analysis of mCRPC patients treated in the COU-AA-302 trial was carried out (NCT00887198).

Outcome measurements and statistical analysis: The Armstrong prognostic model was applied to patients treated in COU-AA-302. A continuous risk score was derived from coefficients from the original model. Time-dependent area under the curve (tAUC) was used to evaluate the overall predictive ability of the model. Patients were categorized according to the number of risk factors present into those at a low (three or fewer risk factors), intermediate (four to six risk factors), and high (seven to ten risk factors) risk. The association with survival was assessed with Cox regression models. Interaction tests were used to assess the impact of treatment arm in each of the prognostic groups.

Results and limitations: A total of 1088 patients were analyzed. The risk score was associated with overall survival (OS; tAUC 0.733). Most patients were at a low (49%) or intermediate (41%) risk. Risk category was significantly associated with OS (hazard ratio [HR]: 2.3; 95% confidence interval [CI]: 1.9-2.4; p < 0.001), radiographic progression-free survival (rPFS; HR: 1.7; 95% CI: 1.5-1.8; p < 0.001), and prostate-specific antigen progression-free survival (HR: 1.7; 95% CI: 1.5-1.9; p < 0.001). A significant interaction between risk group and OS (p = 0.007) and rPFS (p = 0.009) was observed. Survival was superior in low-risk patients (HR: 0.73; 95% CI: 0.59-0.89; p = 0.009), but similar in intermediate-risk (HR: 0.97; 95% CI: 0.79-1.21; p = 0.9) and high-risk (HR: 1.35; 95% CI: 0.80-2.28; p = 0.5) patients. Two-year OS rates in abiraterone versus placebo were 82% versus 74% in low-risk, 55% versus 52% in intermediate-risk, and 28% versus 31% in high-risk patients.

Conclusions: We validate the prognostic value of the Armstrong risk model in patients treated with first-line androgen receptor signaling inhibitors. Abiraterone provided a greater benefit in low-risk patients with less aggressive disease. Further research is needed to establish the role of Armstrong risk groups for treatment selection in mCRPC patients.

Patient summary: In this report, we validated the Armstrong nomogram in the COU-AA-302 trial population. We found a similar prognostic performance to that of the original model. Good-risk patients received the greatest benefit from abiraterone.

Keywords: Abiraterone; Enzalutamide; Hormone therapy; Metastatic castration-resistant prostate cancer; Nomogram; Predictive; Prognostic; Quality of life; Survival.