In prostate cancers, 40-80% of tumors harbor a gene fusion between the androgen receptor (AR)-responsive transmembrane protease serine 2 (TMPRSS2) gene and E26 transformation-specific (ETS) family transcription factor, most often the oncogene ETS-related gene (ERG) (Tomlins et al. 2005). The gene discussed is TMPRSS2; the disease is prostate cancer.