The first recurrent translocation event in prostate cancer has been recently described; it results in the translocation of an ETS (E26 transformation specific) transcription factor (ERG or ETV1) to the TMPRSS2 promoter region, which contains androgen responsive elements. The TMPRSS2:ERG genetic rearrangement has been reported to occur in approximately 40% of primary prostate tumours (ETV1 genetic rearrangements occur at a much lower frequency), and it results in the aberrant androgen-regulated expression of ERG. Tomlins et al. concluded that ETS genetic rearrangements are sufficient to initiate prostate neoplasia. However, here we show that ETS genetic rearrangements may in fact represent progression events rather than initiation events in prostate tumorigenesis. To this end, we demonstrate that the prostate-specific overexpression of ERG does not initiate prostate tumorigenesis.