In Tmprss2-ERG;Nkx3.1+/- (or -/-) male mice, although we observed a slight but significant upregulation of Tmprss2-ERG fusion expression upon Nkx3. 1 loss, we did not detect any significant cooperation between these two genetic events to enhance prostate tumorigenesis in vivo. The gene discussed is ERG; the disease is prostatitis.