[57] Immunohistochemical Profile of 494 Genetically-Confirmed Ewing's Sarcoma Cases

Antonio Llombart-Bosch, Isidro Machado, Marco Alberghini, Samuel Navarro. University of Valencia, Valencia, Spain; Orthopedic Institute Rizzoli, Bologna, Italy

Background: Ewing's sarcoma family of tumors (ESFT) represents a well established clinical, morphological and molecular entity. The aim of the present study is to describe the complete immunohistochemical profile in a large series of genetically-confirmed ESFT.
Design: A total of 494 genetically-confirmed ESFT were included in the study. The tumors were divided according to the histological subtypes into conventional, PNET and atypical variants. Immunohistochemical analysis was performed on tissue microarray sections using antibodies to determine mesenchymal/neural (CD99,Fli1,HNK-1,Cav-1,S100), epithelial (pan-CK, CK20,EMA,CEA), neuroendocrine (synaptophysin, chromogranin-A, NF) and/or myogenic differentiation (actin, desmin, myogenin). A correlation between IHC expression and histological subtypes was achieved.
Results: CD99, HNK-1, CAV-1 and Fli1 were the most positively expressed antibodies in the present series. Epithelial differentiation (pan-CK) was observed in 19.2% of tumors, mainly in the atypical variant. CK20 was absent in all cases, however EMA and CEA were seen in 6.6% and 20.8% of ESFT respectively, and also predominantly in the atypical subtype. ESFT did not reveal desmin or myogenin. A low proportion of neuroendocrine markers were expressed.
Conclusions: The accurate diagnosis of ESFT has been supported by genetic analysis and immunohistochemical profiling, mainly represented by positivity to CD99, Fli1, HNK-1 and CAV1. The epithelial expression including EMA and/or CEA positivity in small round cell tumor does not exclude the diagnosis of ESFT. Presence of a myogenic differentiation should rule out the diagnosis of this entity. The atypical ESFT present immunohistochemical features that overlap with other small round cell tumors, thus molecular studies should be used in order to attain an accurate diagnosis.
Supported by EuroBoNet Grant Nº 018814 and Red de tumores Infantiles. *RD06/0020/0102 Instituto de Salud Carlos III, Madrid
Category: Bone & Soft Tissue

Monday, March 19, 2012 1:00 PM

Poster Session II # 2, Monday Afternoon


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