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WHO Classification of Tumours
Ewing sarcoma


A small round cell tumor that lacks morphologic, immunohistochemical, and electron microscopic evidence of neuroectodermal differentiation. It represents one of the two ends of the spectrum called Ewing's sarcoma/peripheral neuroectodermal tumor. It affects mostly males under age 20, and it can occur in soft tissue or bone.

Tumours of this family (peripheral primitive neuroectodermal tumours [PNETs]) have been reported in the pancreas

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Movahedi-Lankarani S, Hruban RH, Westra WH, Klimstra DS (2002)
Primitive neuroectodermal tumors of the pancreas: a report of seven cases of a rare neoplasm.
Am J Surg Pathol 26: 1040-7

. These small round blue cell tumours have rearrangement of the EWSR1 gene, usually a EWSR1-FLI1 fusion with t(11;22) translocation, and are strongly immunoreactive for CD99. They often express synaptophysin, and occasionally keratins. Before making a diagnosis of Ewing sarcoma, other small round blue cell tumours and pancreatic neuroendocrine neoplasms must be excluded
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Hruban RH, Pitman MB, and Klimstra DS
Tumors of the Pancreas. Armed Forces Institute of Pathology
Washington, DC 2007

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Bosman FT, Carneiro F, Hruban RH, Theise ND (Eds.)
WHO Classification of Tumours of the Digestive System.
4th Edition
International Agency for Research on Cancer: Lyon 2010