[873] Immunohistochemical Evaluation of TMPRSS2-ERG Gene Fusion in Adenosis of the Prostate

Whitney M Green, Jessica L Hicks, Angelo DeMarzo, Jonathan I Epstein. The Johns Hopkins Hospital, Baltimore

Background: Adenosis (atypical adenomatous hyperplasia) is a benign lesion that morphologically mimics prostate adenocarcinoma. To date, there is no convincing evidence that adenosis is a precursor lesion to prostate adenocarcinoma, although the relationship between these two lesions is still debated. The TMPRSS2-ERG fusion has recently been identified as a common chromosomal rearrangement which occurs early in the development of invasive adenocarcinoma of the prostate. This fusion is present in 50% of adenocarcinoma and 20% of high-grade prostatic intraepithelial lesions. Until recently, FISH was the only method available to detect these rearrangements. There is near perfect association between the ERG gene rearrangements and expression of truncated ERG protein. A specific anti-ERG antibody is now available that has 95.7% sensitivity and 96.5% specificity for detecting ERG protein expression, thus serving as a useful marker for ERG rearrangements. Here, we utilized this antibody to further evaluate the relationship between adenocarcinoma and adenosis of the prostate.
Design: We performed a search of the JHH pathology database to identify cases of prostate biopsies, transurethral resections of the prostate (TURP), and radical prostatectomies which included adenosis in the final diagnosis. Slides were immunostained for ERG. Quality control was assessed by examining endogenous endothelial cells as an internal positive control. The pattern of ERG staining was then assessed in adenosis.
Results: In this preliminary study, 26 cases including 15 (58%) biopsies, 7 (27%) TURPs, and 4 (15%) radical prostatectomies were evaluated by IHC for ERG expression. The quality of the stain was adequate in 100% of the cases as evidenced by staining of the positive internal controls. Although we confirmed the presence of adenosis in all cases, no foci of adenosis were positive for ERG protein expression.
Conclusions: In this preliminary study, 26 cases of adenosis were indirectly evaluated for TMPRSS2-ERG rearrangement by ERG immunostaining and none of these cases showed ERG protein expression. We are in the process of gathering additonal consult cases of adenosis for IHC analysis of ERG expresssion. If our initial findings corroborate that ERG expression is not observed in adenosis, it supports the notion that adenosis is not a precursor lesion of adenocarcinoma. Moreover, these results suggest that positive IHC for ERG could be a useful marker to exclude a diagnosis of adenosis.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 155, Monday Afternoon


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