ERG immunostaining is highly specific for prostatic adenocarcinoma

Abstract

<h3>Aims</h3> Immunohistochemistry for ERG has been reported to be highly sensitive and specific for the TMPRSS2-ERG fusion onco-gene. This fusion oncogene has been found in 50–70% of prostate cancers in screened populations but rarely to never in benign disease. We sought to assess the sensitivity and specificity of immunohistochemistry for ERG for the diagnosis of prostate carcinoma in an Australian population. <h3>Methods</h3> A TMA was constructed containing material from 283 consecutive prostatic adenocarcinomas from radical prostatectomies. Immunohistochemistry was performed with a mouse monoclonal antibody directed against ERG (clone 9FY Biocare Medical, USA). <h3>Results</h3> ERG staining was positive in 146 adenocarcinomas (51.5%). There was no staining of benign glands (specificity 100%). Commonly high grade PIN (HGPIN) adjacent to adeno-carcinoma showed positive staining, but in only two cases was there positive staining in PIN without there being ERG positive carcinoma present in the same TMA core. <h3>Conclusions</h3> ERG shows a sensitivity of 51.5% and a remarkable specificity of 100% for the diagnosis of prostatic adenocarcinoma versus benign glands. ERG positive PIN is almost always associated with invasive adenocarcinoma in the same core biopsy. Immuno-histochemistry for ERG may therefore have significant role in the pathological differential diagnosis of difficult prostate biopsies.