[872] ERG vs. Alpha-Methylacyl-CoA Racemase Expression in Histologic Variants of Adenocarcinoma of the Prostate

Srinivas Gottipati, Jena Hudson, Peter Humphrey. Washington University, Saint Louis, MO

Background: The utility of the widely used p63/34βE12/alpha-methylacyl-CoA racemase (AMACR) triple stain immunohistochemistry (IHC) can be limited in some variants of prostate adenocarcinoma (PC) including atrophic, foamy gland and pseudohyperplastic PC, where almost a third of these variants do not express AMACR. The recent discovery of TMPRSS2: ERG gene rearrangement in PC and the subsequent development of a highly specific antibody to ERG have generated considerable interest in ERG IHC as an aid in detecting prostate cancers. However, added diagnostic value of ERG expression beyond AMACR expression has not been addressed. The aim of the study was to investigate whether ERG IHC can provide an advantage in diagnosis of these deceptively benign-appearing variants.
Design: 97 radical prostatectomy cases of variant PC, including atrophic, foamy gland, and pseudohyperplastic (PH) adenocarcinomas were selected from our files. All cases had both variant adenocarcinoma and usual acinar adenocarcinoma components. H&E, triple stain with AMACR, and ERG IHC stains were obtained. Both the intensity (0-3) and the percentage of glands stained (1-4)were scored, generating an IHC score ranging from 0-12 for both ERG and AMACR expression. We searched for areas that were either completely negative or stained weakly for AMACR and compared these foci with ERG IHC to assess for difference in comparative staining.
Results: 50 of the 97 cases were positive in ERG IHC. Both ERG and AMACR antibodies marked usual acinar adenocarcinoma with greater intensity as compared to the variants. 15 cases had foci which were completely negative for AMACR including 12 foamy glands, 6 atrophic, 3 pseudohyperplastic, and 4 usual acinar adenocarcinoma foci; these foci were strongly positive with ERG. 16 cases showed significantly weaker staining with AMACR as compared to ERG in foci of variants and usual acinar adenocarcinoma of which there were 10 foci each of usual acinar and foamy glands and 5 foci of atrophic glands. The IHC scores of ERG/AMACR in these 31 cases was 11.6/8.3 for usual acinar, 11.2/6.2 for atrophic, 10.8/6.8 for microcystic, and 9.9/5.2 for foamy gland foci. In 2 cases AMACR was positive in ERG negative foci, which included one focus each of usual acinar and foamy gland PC.
Conclusions: ERG immunostains provide added value beyond AMACR immunostains in a substantial number of cases of prostatic adenocarcinoma with atrophic, foamy gland, and pseudohyperplastic variant histological appearance, that can be deceptively-benign appearing.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 131, Monday Morning

 

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