TMPRSS2:ERG Gene Fusion Predicts Subsequent Detection of Prostate Cancer in Patients With High-Grade Prostatic Intraepithelial Neoplasia

High-grade prostatic intraepithelial neoplasia (HGPIN) is considered a precursor lesion of prostate cancer (PCa). The predictive value of ERG gene fusion in HGPIN for PCa was interrogated as a post hoc analysis in the context of a randomized clinical trial. The GTx Protocol G300104 randomly assigned 1,590 men with biopsy-diagnosed HGPIN to receive toremifene or placebo for 3 years or until a diagnosis of PCa was made on prostate biopsy. As part of this phase III clinical trial, a central pathologist evaluated biopsies of patients with isolated HGPIN at baseline and 12, 24, and 36 months of follow-up. ERG immunohistochemistry was performed on biopsies from 461 patients and evaluated for protein overexpression. ERG expression was detected in 11.1% of patients (51 of 461 patients) with isolated HGPIN. In the first year and during the 3-year clinical trial, 14.7% and 36.9% of 461 patients were diagnosed with PCa, respectively. Patients with ERG expression were more likely to develop PCa, with 27 (53%) of 51 ERG-positive and 143 (35%) of 410 ERG-negative patients experiencing progression to PCa (P = .014, Fisher's exact test). ERG expression was not associated with age, baseline PSA, Gleason score, or tumor volume. This study underscores the necessity of more stringent follow-up for men with HGPIN that is also positive for ERG overexpression. Clinicians should consider molecular characterization of HGPIN as a means to improve risk stratification.