[1024] The Utility of ERG Antibody in the Assessment of Difficult Prostate Biopsies: How Often Does ERG Contribute to Resolving an Atypical Diagnosis beyond That Provided by Basal Cell Markers and AMACR?

Yousef Tadros, Brenda Brummell, Ming Zhou, Rajal B Shah. Caris Life Sciences, Irving, TX; Cleveland Clinic, Cleveland, OH

Background: Recent studies have demonstrated high correlation between ERG protein expression with the TMPRSS2: ERG gene fusions, a specific molecular event seen in ∼50% of prostate cancers and ∼20% of HGPIN lesions intermingled with adjacent adenocarcinoma demonstrating identical gene fusions. We evaluated the diagnostic utility of ERG antibody in resolving difficult prostate biopsies beyond that provided by routinely utilized cancer marker AMACR and basal cell markers.
Design: 96 prostate needle biopsies with “atypical” glandular proliferation were stained with ERG (clone EPR3864), AMACR and basal cell cocktail antibodies. ERG and AMACR staining in atypical glands and adjacent benign/PIN glands was graded as negative or positive. For AMACR, only staining that was significantly stronger than that of background benign glands was considered positive. An initial consensus diagnosis was rendered as benign, atypical or cancer based on combined morphology, basal cell markers and AMACR. The impact of ERG antibody on this work up was than independently evaluated based on final interpretation.
Results: A total 72 biopsies with atypical glands were available for review for all markers. A final diagnosis benign, atypical and cancer was rendered following review of morphology and all markers in 7, 21, and 44 cases, respectively. Of 44 cancer diagnoses, 18 (42%) were positive for ERG, and 40(93%) were positive for AMACR. Of 21 atypical diagnoses none were positive for ERG and 18 (81%) were positive for AMACR. Of 6 benign diagnoses, none were positive for ERG and 5 (83%) were positive for AMACR. ERG expression in PIN glands was noted in 8 cases containing adjacent ERG positive(11%) and 1 ERG negative cancer(1%), while AMACR expression was noted in non-cancer glands in all diagnostic categories with a total of 21 (29%) cases. Positive ERG staining converted an initial atypical diagnosis to a final cancer diagnosis in 4/72 (6%) of cases and strengthened the cancer diagnosis in additional 5 cases (7%) where morphology was less than optimal despite AMACR expression and lack of basal cell staining.
Conclusions: ERG has limited independent advantage over traditionally utilized AMACR and basal cell markers. However, in small proportion of cases positive ERG expression helps establish a definitive cancer diagnosis. We propose utilization of ERG as a component of cocktail antibodies in optimal evaluation of difficult prostate biopsies.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 170, Monday Afternoon

 

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