To shed light on the transcriptional regulation of androgen biosynthetic enzymes in tumors, we have previously shown that ERG factor regulates key enzymes in androgen synthesis [11]; thus, TMPRSS2-ERG fusion positive cancer cells producing intracellular androgens are better responders to abiraterone therapy Herein, we extended this concept to in vivo tumor studies. The gene discussed is TMPRSS2; the disease is neoplasm.