[76] Utility of a Monoclonal ERG/FLI1 Antibody for Immunohistochemical Discrimination of Ewing's Family Tumors

Scott A Tomlins, Nallasivam Palanisamy, John C Brenner, Jennifer N Stall, Dafydd G Thomas, Javed Siddiqui, David R Lucas, Arul M Chinnaiyan, Lakshmi P Kunju. University of Michigan Medical School, Ann Arbor, MI

Background: Ewing family tumors (EFTs; Ewing sarcoma/peripheral neuroectodermal tumors) and prostate carcinomas (PCa) are characterized by recurrent rearrangement of ETS family members, including FLI1 (EFTs), ERG (PCa>>EFTs) and less commonly ETV1, ETV4 and ETV5. Previously, we characterized an antibody against ERG (EPR3864) as showing diagnostic utility for the detection of ERG rearranged PCa. More recently, this antibody was shown to cross react with FLI1; thus, here we evaluate the utility of EPR3864 immunostain for discrimination of EWTs from other small round blue cell tumors (SRBCTs).
Design: Western blotting using EPR3864 was performed on EFT cell lines harboring EWS:ERG or EWS:FLI1 fusions. ERG/FLI1 staining by immunohistochemistry (IHC) was evaluated on a TMA with 111 EFT cases from 89 patients, on individual sections of 2 additional EFTs, and on 61 other SRBCTs. Nuclear ERG staining was scored as 0 (negative), 1+ (weak), 2+ (moderate) and 3+ (strong). Staining of vessels was used as a positive control. EFTs were also evaluated for CD99 expression, which was scored as negative or positive (cytoplasmic or membranous).
Results: By Western blotting using EFT cell lines, we demonstrate that EPR3864 detects both EWS:FLI1 and EWS:ERG. Of 53 EFTs evaluable by IHC, 44 (83%) demonstrated at least 2+ diffuse nuclear ERG/FLI1 staining, of which 1, 4 and 39 showed negative, cytoplasmic or membranous CD99 staining, respectively. Of the remaining 9 EFTs with 0-1+ ERG/FLI1 staining, 3, 2 and 4 showed negative, cytoplasmic or membranous CD99 staining, respectively. Amongst other SRBCTs, at least 2+ diffuse nuclear staining was seen in 0 of 11 (0%) Wilm's tumors, 0 of 11 (0%) neuroblastomas, 0 of 7 (0%) alveolar/embryonal rhabdomyosarcomas, 0 of 4 (0%) desmoplastic small round cell tumors, 1 of 10 (10%) Burkitt's lymphomas, 5 of 11 monophasic synovial sarcomas (45%) and 7 of 7 (100%) of precursor-B-lymphoblastic lymphomas/leukemias.
Conclusions: EPR3864 has high sensitivity for EFTs, consistent with reported rates for other anti FLI1 polyclonal and monoclonal antibodies, and is highly correlated with CD99 expression. Amongst other SRBCTs, EPR3864 also stained all precursor-B-lymphoblastic lymphomas/leukemias and a subset of Burkitt's lymphomas and synovial sarcomas, suggesting the need for additional IHC/molecular tests to differentiate these diagnoses. Our results suggest that EPR3864 may have utility in the differentiation of EFTs from other SRBCTs, in addition to its reported utility in PCa.
Category: Bone & Soft Tissue

Monday, March 19, 2012 1:00 PM

Poster Session II # 4, Monday Afternoon


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