[1027] ERG Immunohistochemistry in Prostatic Small Cell Carcinoma: Comparison to Fluorescence In Situ Hybridization

Lindsay A Schelling, Shaobo Zhang, Sean Williamson, Jorge Yao, Mingsheng Wang, Jiaoti Huang, Rodolfo Montironi, Antonio Lopez, Adeboye O Osunkoya, Gregory MacLennan, Liang Cheng. Indiana University School of Medicine, Indianapolis, IN; University of California at Los Angeles, Los Angeles, CA; Polytechnic University of the Marche Region, United Hospitals, Ancona, Italy; Cordoba University, Cordoba, Spain; Emory University, Atlanta, GA; Case Western Reserve University, Cleveland, OH

Background: Due to morphologic and immunohistochemical similarities, small cell carcinoma (SMCC) arising from the prostate can be difficult to distinguish from SMCC arising from other organs, especially the urinary bladder. Recent studies have shown the presence of the TMPRSS2-ERG fusion gene to be specific for prostate carcinoma, and antibody to the ERG protein product has been found to correlate well with the presence of the gene fusion.
Design: We evaluated 30 cases of SMCC of the prostate and compared them to 25 cases of urinary bladder SMCC. Each case was evaluated for the presence of the TMPRSS2-ERG fusion gene by fluorescence in situ hybridization (FISH) and compared to immunohistochemical staining with the ERG antibody.
Results: Of the 30 cases of prostatic SMCC, 14 (47%) were positive for the TMPRSS2-ERG gene fusion by FISH and 6 (20%) were positive for ERG by immunohistochemistry (IHC). Of the 14 cases positive by FISH, 5 (35%) were positive by IHC, while 1 (7%) was positive by IHC but negative by FISH. In cases with a concurrent component of prostatic acinar adenocarcinoma, IHC showed concordant staining in both components. All cases of urinary bladder SMCC were negative for ERG by IHC and FISH.
Conclusions: Immunohistochemical staining for ERG is a useful adjunctive tool for detection of the TMPRSS2-ERG fusion in SMCC of the prostate, although sensitivity appears somewhat decreased compared to molecular methods, and results that have been reported for prostatic adenocarcinoma in general. SMCC of the urinary bladder is negative for the ERG protein product by IHC and therefore ERG IHC may be a useful tool in confirming the prostatic origin of SMCC with unknown primary, particularly when molecular testing is not accessible.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 11:15 AM

Proffered Papers: Section A, Tuesday Morning


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