The cytology of extraskeletal Ewing sarcoma

BACKGROUND, Extraskeletal Ewing sarcoma (EES) shares histologic, immunohist ochemical, and molecular findings with ES of bone. The authors' goal in con ducting this study was to examine the cytomorphologic features of EES. In a ddition, immunocytostaining for CD99/O13 was performed in all cases, and cy togenetic and molecular data were available in al,out half of the cases. METHODS. The authors studied 20 aspiration cases, all with histopathologic confirmation, and also conducted immunohistochemistry and/or molecular stud ies. RESULTS. AU cases had cellular smears with many single cells and focal clus tering. Numerous naked nuclei and focal crush artifacts were seen. Mitosis and necrosis were rare. Four cases had cytoplasmic vacuoles. Five cases sho wed nuclear molding. Seventeen cases (85%) exhibited small cells with scant y cytoplasm and nuclei with fine chromatin and small nucleoli, representing the so-called typical variant. One case (5%) revealed cells with abundant cytoplasm, large nuclei, and large eosinophilic nucleoli, an example of the atypical or large cell variant. Two cases (10%) had features in between, w ith cells showing a fair amount of cytoplasm and medium-sized nucleoli, rep resenting the intermediate variant. Nuclear grooves, described as common in the latter, were rare. In all cases, in either cytologic or corresponding histologic material, CD99/O13 immunocytostaining showed strong membranous r eactivity. In addition, cytogenetic and/or molecular evidence of ES specifi c chromosomal translocation was demonstrated in histologic or cytologic mat erial in 10 cases. CONCLUSIONS, EES shows cytologic features similar to ES of bone, with a spe ctrum of changes ranging from the typical appearance in a majority of cases to intermediate and atypical variants in a minority of cases. CD99/O13 imm unocytostaining and/or molecular studies, particularly in the intermediate and atypical variants, may help in establishing a definitive fine-needle as piration diagnosis, thus avoiding an open surgical biopsy. (C) 1999 America n Cancer Society.