[1009] Antibody Based Detection of ERG Gene Fusions in Prostate Cancer: An Immunohistochemical Study Comparing C- and N-Terminus ERG Antibodies

Rajal B Shah, Robert Lonigro, Brenda Brummell, Javed Siddiqui, Betsy Spaulding, Arul Chinniayan, Rohit Mehra. Caris Life Sciences, Irving; University of Michigan, Ann Arbor, MI; Dako Corporation, Carpentaria; Memorial Sloan Kettering Cancer Center, New York

Background: TMPRSS2: ERG gene fusion, a highly specific molecular event is seen in ∼50% of prostate cancers (PCa) and ∼20% of HGPIN lesions intermingled with adjacent PCa demonstrating identical gene fusions. Recent studies have demonstrated excellent correlation between positive immunohistochemical (IHC) reaction with novel ERG antibody and underlying ERG gene rearrangement in PCa. The goal of this study is to compare the sensitivity of two commercially available antibodies (C- and N- terminally directed) for detection of gene fusion positive PCa and to correlate ERG protein expression with molecular class of gene fusions.
Design: A tissue microarray (TMA) containing 294 cores from 93 patients with PCa was analyzed using ERG FISH 3' and 5' break apart probes and were classified as negative, rearranged with insertion or deletion mechanism or amplified. IHC was performed using clone EPR3864 generated to C-terminus (aa 393-479) and clone 9FY produced to the N-terminus (aa 42-66) of the ERG protein. The antibodies were optimized using serial dilutions and the immunostaining was compared on TMAs. The patient was classified as positive for ERG if at least one PCa core from that patient had any nuclear staining. Status of ERG protein expression was correlated with presence of gene fusions and molecular class of gene fusions.
Results: A total of 73 patients (290 and 285 cores for C- and N-terminal antibodies respectively) had both FISH and antibodies results available. A total of 41/43 (95%) PCa with gene fusions showed predominantly strong ERG IHC staining with the C-terminal antibody while 10/43 (24%) of PCa with gene fusions showed variable staining results using N-terminal antibody ERG expression (sensitivity 95% versus 24%, p<0.001). Both C- and N-terminus ERG antibodies were not associated molecular class of gene fusions.

AntibodyInsertion (%)Deletion (%)Not rearranged (%)
C-terminus24/25(96)17/18(94)3/30(10)
N-terminus8/25(32)2/18(11)1/29(3)
Comparisons of ERG protein expression by C- and N-terminus antibodies in different classes of gene fusions


Conclusions: The monoclonal antibody directed against C-terminus of ERG was shown to be significantly more sensitive than an antibody to N-terminus for the detection of gene fusion regardless of underlying class of gene fusions. We propose the use of C-terminally directed antibody for optimal antibody based evaluation of gene fusions in prostate cancer.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 151, Monday Afternoon

 

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