TMPRSS2 and prostate cancer: Since the discovery of a recurrent gene fusion between the androgen responsive gene TMPRSS2 (transmembrane protease, serine 2) and ERG (v-ets erythroblastosis virus E26 homolog (avian)) on chromosome 21 [2], prostate cancers are molecularly divided into "fusion-positive" and "fusion-negative" cancers.