[843] Concordance of TMPRSS2-ERG Fusion Status by Quantitative PCR with ERG Protein Expression by Immunohistochemistry Using Anti-ERG Monoclonal Antibody EPR3864

Sara M Falzarano, Carl Millward, Tara Maddala, Diana B Cherbavaz, Mark Lee, Eric A Klein, Cristina Magi-Galluzzi. Cleveland Clinic, Cleveland, OH; Genomic Health, Inc, Redwood City, CA

Background: TMPRSS2-ERG, the most common gene fusion in prostate cancer (PCA), is associated with expression of a truncated protein product of the oncogene ERG. We recently demonstrated that ERG detection by immunohistochemistry (IHC) in PCA was highly predictive of ERG rearrangement as assessed by FISH. The objective of the current study was to compare ERG IHC with TMPRSS2-ERG fusion mRNA expression by quantitative PCR in a large cohort of patients treated with radical prostatectomy (RP) for clinically localized PCA.
Design: 187 RP specimens from patients with clinical stage T1/T2 PCA treated with RP between1987-2004 were included in the study. RNA was extracted from manually dissected formalin-fixed paraffin-embedded sections obtained from selected RP blocks and expression of TMPRSS2-ERGa and TMPRSS2-ERGb was quantified using RT-PCR. A prespecified cutpoint was used to classify samples as fusion positive or negative. The same RP blocks were used to build 10 Tissue Microarrays (TMA) composed of three representative 1.5 mm tissue cores from each tumor using the antibody EPR3864. Any nuclear staining was considered indicative of ERG expression. Endothelial cells were used as a positive control because they are strongly positive for ERG. To compare the accuracy of IHC ERG protein detection in determining the TMPRSS2-ERG fusion status with assessments by RT-PCR (standard reference), sensitivity, specificity, positive (PPV) and negative (NPV) predictive values, with corresponding 95% confidence intervals (CI) were calculated.
Results: TMPRSS2-ERGa and/or TMPRSS2-ERGb fusions were present in 110 (59%) analyzed tumors by RT-PCR. ERG IHC was detected in 112 (60%) tumors, 106 (95%) of which were positive for fusion by RT-PCR. We identified 6/112 (5%) tumors demonstrating ERG protein expression without any of the TMPRSS2-ERG fusions as assessed by RT-PCR. Conversely, 4/110 (4%) cases with TMPRSS2-ERG fusions by RT-PCR had no detectable ERG protein expression in any of the informative cores. ERG IHC was highly concordant with the TMPRSS2-ERG RT-PCR, with a sensitivity of 96% (95% CI: 91%-99%), specificity 92% (84%-99%), PPV 95% (89%-98%), and NPV 95% (87%-99%).
Conclusions: ERG detection by IHC showed a high concordance with TMPRSS2-ERG mRNA overexpression measured by RT-PCR in a large cohort of RP patients. The consistency of these results supports the utility of both methods for assessing TMPRSS2-ERG fusion status. IHC may be a useful adjunctive tool since it is easier to perform and less costly.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 168, Monday Afternoon

 

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