The transmembrane protease, serine 2-E twenty-six related gene (TMPRSS2-ERG) fusion leading to ERG overexpression, was detected in approximately 50% of prostate cancers (ranging from 35-70%). However, the published data on ERG expression in tumors from other organs and normal tissues were limited. In this study, we investigated the expression of ERG in TMA sections of various normal tissues (N=452) and carcinomas (N=1,129) from various organs, including 90 cases of low to intermediate-grade (L-MG) prostatic adenocarcinomas and 36 cases of high-grade (HG) prostatic adenocarcinomas, using a single immunostaining system (Dako). Also included were prostatic biopsies of radiation atypia (N=20), atrophy (N=20), and high-grade prostatic intraepithelial lesion (HGPIN) (N=18). ERG expression was detected in 44% (40/90) of L-MG prostatic adenocarcinomas; in 22% (8/36) of HG prostatic adenocarcinomas; and in 22% (4/18) of HGPIN. No ERG expression was detected in non-prostate carcinomas, normal tissues including prostate and seminal vesicles, benign prostatic tissue with radiation atypia, and atrophy. Our data demonstrate that ERG is a highly specific marker, which may have important implications in the interpretation of prostate biopsies with limited cancers. In addition, its high diagnostic specificity may be useful in identifying a prostatic primary when working on a tumor of uncertain origin.

Partly presented at the United States and Canadian Academy of Pathology Annual Meeting in March 2011