Cytodiagnosis of Extraskeletal Ewing’s Sarcoma and its Confirmation by Fluorescence in situ Hybridization

A 10-year-old male presented with a right gluteal region mass since a duration of six months. The patient also complained of loss of appetite and dyspnoea. On examination, there was a right gluteal ulcerated mass measuring 10 88 cm [Table There was no lymphadenopathy or organomegaly. X-ray of the right pelvic region revealed a soft tissue mass measuring 21x10 cm, not involving the underlying bone [Table/ Fig-1b]. Contrast enhanced computed tomography showed an exophytic heterogenous soft tissue mass measuring 21.8x10 cm arising from right gluteus maximus muscle. FNAC was performed and smears were stained for May-Grunwald Giemsa (MGG) and Papanicolaou (Pap) stains, and material was collected for cell block preparation. Cytology smears were cellular and showed dispersed, small, monomorphic round cells with fine nuclear chromatin, round nuclei and scanty clear cytoplasm [Table/Fig-2a,b]. Many cells showed irregularly vacuolated cytoplasm. Occasional rosette formation was also seen [Table/Fig-2c]. Immunocytochemistry showed tumour cells positive for CD99 and negative for desmin, Leucocyte Common Antigen (LCA) and TdT [Table/Fig-2d]. Based on these cytological and IHC features, a diagnosis of extraskeletal Ewing's sarcoma was offered. The cell block sections showed sheets of small round cells with rosette formation [Table/Fig-3a]. Immunohistochemistry (IHC) markers were performed on cell block, which showed membranous positivity for CD99 and nuclear positivity for Friend leukaemia integration-1 (FLI1) [Table/Fig-3b,c]. The tumour cells were negative for Pancytokeratin, Bcl2, desmin, MyoD1, LCA, TdT, chromogranin, Neuron specific enolase (NSE)