The most frequent of these rearrangements create a TMPRSS2-ERG fusion gene, observed in ~15% of prostate intraepithelial neoplasia (PIN) and in ~50% of localized prostate cancer: this observation suggests that this genetic anomaly may represent an early event predisposing to tumor progression [101]. The gene discussed is ERG; the disease is prostate intraepithelial neoplasia.