Serum Androgens as Predictive Biomarkers: Results From a Randomized Clinical Trial Comparing Enzalutamide and Abiraterone Acetate in Men With Metastatic Castration-Resistant Prostate Cancer

Introduction

The purpose of this study was to investigate the association between baseline androgen concentrations and outcomes in men with metastatic castration-resistant prostate cancer (mCRPC) treated with first-line enzalutamide or abiraterone acetate plus prednisone (AAP).

Materials and Methods

We previously randomized men with mCRPC to enzalutamide or AAP to compare side-effects and measured androgen concentrations. In this post-hoc analysis, patients were grouped in quartiles (Q) based on their serum androgen values. Kaplan-Meier and Cox regression were used to analyze progression-free and overall survival for baseline androgen groups, treatment subgroups and their interaction. The trial was registered at clinicaltrialsregister.eu (2017-000099-27).

Results

Eighty-four patients received enzalutamide and 85 AAP. Overall, higher (Q4) compared with lower (Q1) baseline serum testosterone was associated with longer progression-free survival (24.8 vs. 10.7 months, hazard ratio [HR] 0.52, 95% confidence interval [CI] 0.33; 0.84) and overall survival (52.8 vs. 31.5 months, HR 0.49, 95% CI 0.28; 0.85). The risk reduction in death seemed to be treatment dependent (treatment subgroup interaction P = .04). For men in the AAP subgroup, the Q4 compared with Q1 group had a significant lower risk of death (HR 0.30, 95% CI 0.13; 0.73), while no difference was found for enzalutamide (HR 0.77, 95% CI 0.35; 1.69). Similar results were found for the other androgens.

Conclusion

Pre-treatment serum testosterone levels may be a clinically useful biomarker for predicting mCRPC treatment responses and guiding treatment selection.