Association of ERG and TMPRSS2-ERG with grade, stage, and prognosis of prostate cancer is dependent on their expression levels

Background: There is controversy in the literature on the role of the fusion TMPRSS2-ERG in the pathogenesis and progression of prostate cancer. The quantitative differences in TMPRSS2-ERG fusion expression have received very limited attention in the literature.

Methods: We have quantitatively analyzed the mRNA levels of TMPRSS2-ERG, ERG, PTEN, and AR (n = 83), as well as ERG immunostaining (n = 78) in a series of prostate tumors.

Results: Among the TMPRSS2-ERG cases (n = 57), high fusion levels were associated with GS ≥8 (P = 0.025). ERG mRNA overexpression was associated with GS ≥8 (P = 0.047), and with stage T3-T4 tumors (P = 0.032). Among the ERG overexpressing cases (n = 54), higher expression levels were found in 92.3% of GS ≥8 tumors (P = 0.02). ERG immunostaining, regardless of staining intensity, was also associated with high stage (P = 0.05). There was a statistical association between ERG immunostaining and PSA progression-free survival (Log Rank test, P = 0.048). Decreased PTEN expression was associated with TMPRSS2-ERG (P = 0.01), ERG mRNA overexpression (P = 0.003) and ERG immunostaining (P = 0.007). Furthermore, decreased PTEN expression, alone (P = 0.041) and also combined with TMPRSS2-ERG (P = 0.04) or with ERG overexpression (P = 0.04) was associated with GS ≥7 tumors.

Conclusions: Although more studies are needed to further clarify their role, our findings emphasize that the expression levels of the TMPRSS2-ERG fusion and ERG mRNA, rather than their mere presence, are related to a more aggressive phenotype, have an effect on prognosis and could be molecular markers of progression for prostate cancer. Furthermore, ERG immunohistochemistry could be also a potentially useful prognostic factor.