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WHO Classification of Tumours
Ewing sarcoma
Bone


Definition

Ewing sarcoma (EWS) and primitive neuroectodermal tumours (PNET) represent a group of small round cell neoplasms with variable degrees of neuroectodermal differentiationis. EWS typically shows little or no neurodectodermal features.The Ewing family of tumours (EFT) is characterized by a recurrent (t11;22)(q24;q12) chromosomal translocation, detectable in approximately 85% of cases that results in an in-frame fusion between the EWS and FLI1 genes.

Ewing sarcoma of bone most frequently arises in the diaphysis or metaphyseal-diaphyseal portion of long bones. The tumours are ill-defined osteolytic lesions and often necrotic and haemorrhagic. Permeative or motheaten bone destruction, frequently associated with "onion-skin"-like multilayered periosteal reaction, is characteristic. The cortex overlying the tumour is irregularly thinned or thickened. .
Ewing sarcoma is the second most common sarcoma of bone and soft tissues in children. It shows a peak incidence in the second decade of life; patients older than 30 years are very rare. The current 5-years survival rate is estimated to be 41%

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Fletcher CDM, Unni KK, Mertens F (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Soft Tissue and Bone.
3rd Edition
IARC Press: Lyon 2002



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