Transmembrane protease serine 2:v-ets erythroblastosis virus E26 oncogene homolog (TMPRSS2-ERG) fusion is the single most frequent genetic alteration in prostate cancer; a fusion of Erythroblast Transformation Specific (ETS) family genes with the protease gene TMPRSS2. The gene discussed is ERG; the disease is prostate carcinoma.