The disclosure describes alterations in ERG gene expression. ERG isoforms and promoter sequence of the ERG gene that are involved in, or associated with, prostate cancer are provided. The disclosure further provides therapeutic compositions and methods of detecting, diagnosing, prognosing, and treating prostate cancer, including biomarkers for detecting the expression of two or more of the following genes: PSA/KLK3, PMEPA1, NKX3.1, ODC1, AMD1, and ERG.