Prognostic Utility of a Whole-blood Androgen Receptor-based Gene Signature in Metastatic Castration-resistant Prostate Cancer.

BACKGROUND: The treatment paradigm for metastatic castration-resistant prostate cancer (mCRPC) has evolved significantly in recent years. Identifying predictive and/or prognostic biomarkers in the context of this rapidly expanding therapeutic armamentarium remains a pressing and unmet clinical need. OBJECTIVE: To develop a prognostic whole-blood gene signature for mCRPC patients. DESIGN, SETTING, AND PARTICIPANTS: As part of an ongoing prospective, multicentre biomarker research study (Australian Prostate Biomarker Alliance), we enrolled 115 mCRPC patients commencing chemotherapy (n = 34) or androgen receptor (AR) pathway inhibitors therapy (n = 81) and obtained pretreatment whole-blood samples in PAXgene RNA tubes. Gene expression was assessed using reverse transcription-polymerase chain reaction. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Gene transcripts correlating with overall survival (OS) at p < 0.10 in univariate Cox regression models were incorporated into a multigene signature. Kaplan-Meier survival estimates and multivariate analyses were used to assess association with clinical outcomes. Prognostic strength of the signature was estimated using a concordance probability estimate (CPE). RESULTS AND LIMITATIONS: Based on univariate analysis for OS, the following genes were incorporated into a multigene signature: AR splice variant 7 (AR-V7), and three androgen-regulated genes: GRHL2, HOXB13, and FOXA1. The number of positive transcripts clearly stratified survival outcomes (median OS: not reached vs 24.8 mo vs 16.2 mo for 0, 1, and ≥2 transcripts, respectively; p = 0.0052). Notably, this multigene signature retained prognostic significance on multivariable analysis (hazard ratio, 2.1; 95% confidence interval, 1.1-4.0; p = 0.019). Moreover, CPE for this model was 0.78, indicating strong discriminative capacity. Limitations include short follow-up time. CONCLUSIONS: Our data demonstrate the prognostic utility of a novel whole-blood AR-based signature in mCRPC patients commencing contemporary systemic therapies. Our pragmatic assay requires minimal processing, can be performed in most hospital laboratories, and could represent a key prognostic tool for risk stratification in mCRPC. PATIENT SUMMARY: We found that expression of certain genes associated with the androgen receptor could help determine how long men with advanced prostate cancer survive after starting modern drug therapies.