[976] Immunohistochemical Evaluation of ERG Expression in Metastatic Carcinoma of the Prostate

Edgardo R Parrilla-Castellar, John C Cheville, Manish Kohli, Thomas J Sebo, Rafael E Jimenez. Mayo Clinic, Rochester, MN

Background: TMPRSS2-ERG is the most common gene fusion occurring in prostate cancer (PCa), and results in the expression of a truncated protein product of the oncogene ERG. Immunohistochemical detection of this protein product has been demonstrated to have a high correlation with TMPRSS2-ERG gene fusion status in primary prostatic tumors. Feasibility of ERG expression assessment and its frequency in metastatic PCa have not been extensively evaluated.
Design: We reviewed 75 cases of metastatic PCa and performed immunohistochemistry for ERG utilizing a monoclonal antibody. ERG expression was evaluated as positive if nuclear staining was observed. Overall survival from date of diagnosis was assessed using the Kaplan-Meier method and the log-rank test. Multivariate analysis was carried-out using a Cox regression model. Clinical end-points included date of death or date of last follow-up.
Results: Metastatic sites of involvement included bone (54%), lung (20%), liver (19%), brain (4%), gastrointestinal tract (1%), bladder (1%), and lymph node (1%). Overall, ERG was positive in 20 cases (27%), including 9/40 bone, 6/16 lung, 2/14 liver, 2/3 brain, 1/1 bladder, and 0/1 colon. Lung cases represented 30% of ERG-positive cases, compared to 18% of ERG-negative case (p=0.341). All tumors showed high-grade morphology (Gleason grade 8-10), and no morphologic features distinguished ERG-positive cases. ERG expression did not correlate with survival in either univariate or multivariate analysis.
Conclusions: Frequency of ERG expression in metastatic PCa is similar to reported rates of TMPRSS2-ERG gene fusion in this setting. ERG positivity is not predictive of site of metastasis or survival after detection of metastasis. Since TMPRSS2-ERG status could potentially influence the modality of systemic therapy, its determination by immunohistochemical evaluation of ERG expression may be a viable and affordable option in patients with metastatic PCa.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 179, Monday Afternoon

 

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