Ishida et al. isolated a HML-2 Gag protein in the serum of a prostate cancer patient using serological recombinant cDNA expression cloning (SEREX) technology.25 They subsequently detected HML-2 gag mRNA in the serum of six of nine prostate cancer patients, but failed to detect HML-2 gag mRNA in LnCAP, DU145 or PC3 prostate cancer cells.25 Gene fusions are a frequent occurrence in prostate cancer, the majority of which involve the fusion of the transcription factors ETS translocation variant (ETV1) or ETS-related gene (ERG1), to the transmembrane protease, serine 2 (TMPRSS2). The gene discussed is ERG; the disease is prostate carcinoma.