Enhancer of zeste-homolog 2 (EZH2) expression and clinical outcomes in metastatic castrate resistant prostate cancer (mCRPC).

Abstract

350 Background: In prostate cancer, overexpression of EZH2 is associated with disease recurrence, androgen independent growth, cell invasion, and metastases. We evaluated the prognostic significance of EZH2 gene expression in metastatic biopsies from men with CRPC. Methods: EZH2 (RNA) expression was evaluated in two serial metastatic site biopsies in patients (pts) prior to treatment with abiraterone acetate and prednisone (pre-AA/P) and after 12 weeks of treatment (post-AA/P). All pts were enrolled and prospectively followed for clinical outcomes. The primary endpoint was overall survival (OS), defined as the time from CRPC to death or last follow-up. Cox proportional hazard regression analysis was performed on EZH2 expression using normalized fragments per kilobase million (FPKM) > 1 for association with OS and time to treatment failure (TTF). Results: Of 92 enrolled pts, 59 pts had (pre-AA/P) gene expression using RNA-seq, 45 had paired pre and post-AA/P RNA-seq available for analysis. In pre-AA/P samples, the median EZH2 expression was 4.82 FPKMs (range 1.05-38.8). Elevated expression of EZH2 was associated with shorter OS [hazard ratio (HR) 2.58, p = 0.016]. Radiographic progression at 12 weeks was more frequent in high EZH2 tumors compared to low EZH2 tumors (48% vs 20%, p = 0.03, Fisher’s exact test) No statistically significant associations were identified between EZH2 expression and TTF. In paired post-AA/P biopsies, EZH2 expression increased in 13/45 tumors and decreased in 32/45 tumors. The median log2 fold change in EZH2 expression was -1.38 (range -6.7 to 3.1). In post-AA/P biopsies, no associations were identified between an increase in EZH2 expression and OS or TTF. Conclusions: EZH2 expression represents a potential novel prognostic biomarker in mCRPC and warrants further exploration. Clinical trial information: 01953640.