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#redirect [[Chondro-osseous tumours#Ewing sarcoma]]
'''Ewing sarcoma''', also known as '''EWS/pPNET''', is an uncommon bone tumour.
 
Confusingly, it is known as EWS/PNET. ''EWS'' is ''Ewing sarcoma''. ''pPNET'' is ''peripheral primitive neuroectodermal tumour''. ''EWS'' and ''pPNET'' were once thought to be different tumours.
 
''Peripheral primitive neuroectodermal tumour'' should not be confused with ''[[primitive neuroectodermal tumour]]'', commonly abbreviated ''PNET'', a (supertentorial) brain tumour with similarities to [[medulloblastoma]].
 
==General==
Clinical:
*Painful.
*Usually younger than 20 years.
*Second most common malignant bone tumour in children.
**Most common malignant bone tumour = osteosarcoma (AKA osteogenic sarcoma).
 
Poor prognostic factors:<ref>PST. 14 February 2011.</ref>
*Age (18 years-old+).
*Pelvis (extremity = good).
*>8 cm.
*[[Metastases]].
*EWS-FL1 fusion type 2.
*>90% [[necrosis]].
 
Etiology:
*Unknown origin; hypothesis: Ewing sarcoma arises from mesenchymal stem cell.<ref name=pmid20953407>{{cite journal |author=Lin PP, Wang Y, Lozano G |title=Mesenchymal Stem Cells and the Origin of Ewing's Sarcoma |journal=Sarcoma |volume=2011 |issue= |pages= |year=2011 |pmid=20953407 |pmc=2952797 |doi=10.1155/2011/276463 |url=}}</ref>
 
===Radiology===
Features:<ref name=Ref_WMSP650>{{Ref WMSP|650}}</ref>
*Long bones, diaphyses.
*Destructive.
*"Onion-skin" periosteal reaction.
 
==Microscopic==
Features:<ref>PST. 22 February 2010.</ref>
*Scant clear cytoplasm (contain glycogen -- PAS +ve, PAS-D -ve) - '''key feature'''.
*Round small nucleus.
**Usu. lack nucleoli.
**Usu. minimal-moderate size variation.
*Mitoses (common).
 
Notes:
*It is a [[small round cell tumour]].
*[[Rhabdomyosarcoma]] occasionally has cytoplasmic clearing (due to glycogen).<ref name=PST14feb11>PST. 14 February 2011.</ref>
 
====Images====
<gallery>
Image:Ewing sarcoma - intermed mag.jpg | ES - intermed. mag.
Image:Ewing sarcoma - high mag.jpg | ES - high mag.
Image:Ewing sarcoma - very high mag.jpg | ES - very high mag.
</gallery>
<gallery>
Image:Ewing sarcoma - PAS - intermed mag.jpg | ES - PAS - intermed. mag.
Image:Ewing sarcoma - PAS - high mag.jpg | ES - PAS - high mag.
Image:Ewing sarcoma - PAS - very high mag.jpg | ES - PAS - very high mag.
</gallery>
www:
*[http://path.upmc.edu/cases/case103.html Ewing sarcoma - case 1 - several images (upmc.edu)].
*[http://path.upmc.edu/cases/case420.html Ewing sarcoma - case 2 - several images (upmc.edu)].
 
==[[IHC]]==
Features:<ref name=Ref_WMSP651>{{Ref WMSP|651}}</ref>
*CD99 +ve -- 1. diffuse, 2. plasma membrane staining; both required -- most specific.
*FLI-1 +ve.<ref name=pmid15001993>{{cite journal |author=Rossi S, Orvieto E, Furlanetto A, Laurino L, Ninfo V, Dei Tos AP |title=Utility of the immunohistochemical detection of FLI-1 expression in round cell and vascular neoplasm using a monoclonal antibody |journal=Mod. Pathol. |volume=17 |issue=5 |pages=547–52 |year=2004 |month=May |pmid=15001993 |doi=10.1038/modpathol.3800065 |url=http://www.nature.com/modpathol/journal/v17/n5/full/3800065a.html}}</ref>
*CD45 -ve.
**Done to r/o [[lymphoma]].
*+/-Neural markers (NSE, synaptophysin, CD57 (??? CD56 ???), S100).
*+/-Cytokeratins.
*Caveolin-1 +ve in ~ 85% of EWS.<ref>PST. 14 February 2011.</ref>
*WT-1 -ve.<ref name=Ref_WMSP286>{{Ref WMSP|286}}</ref>
 
Notes:<ref>PST. 22 February 2010.</ref>
*CD99 +ve
**Plasma membrane staining tumours:
***[[Lymphoblastic lymphoma]]/leukemia.
***[[Angiomatoid fibrous histiocytoma]].
***[[Desmoplastic small round cell tumour]].
**Weak/cytoplasmic staining:
***[[Synovial sarcoma]].
***[[Rhabdomyosarcoma]].
***[[Rhabdoid tumour]].
*FLI-1 +ve:<ref name=pmid15001993/>
**[[Vascular neoplasms]].
**-/+[[Merkel cell carcinoma]].
**-/+[[Melanoma]].
 
==Molecular diagnostics==
Common features:
*''EWS/FLI-1 fusion gene'' formation due to [[translocation]]: ''t(11;22)(q24;q12)''.<ref>URL: [http://atlasgeneticsoncology.org/Tumors/Ewing5010.html http://atlasgeneticsoncology.org/Tumors/Ewing5010.html]. Accessed on: 23 February 2010.</ref><ref name=pmid3163261>{{cite journal |author=Turc-Carel C, Aurias A, Mugneret F, ''et al.'' |title=Chromosomes in Ewing's sarcoma. I. An evaluation of 85 cases of remarkable consistency of t(11;22)(q24;q12) |journal=Cancer Genet. Cytogenet. |volume=32 |issue=2 |pages=229–38 |year=1988 |month=June |pmid=3163261 |doi= |url=}}</ref>
**Often detected by RT-PCR (with EWS 5' and FLI-1 3' primers).
**Type 1 = EWS exon 7 + FLI-1 exon 6; good prognosis.
**Type 2 = others; poor prognosis.
 
Notes:
*The ''t(11;22)(q24;q12)'' is seen in ~90% of EWS/PNET... but also in:
**[[Olfactory neuroblastoma]].
**Small cell osteogenic sarcoma (small cell variant of [[osteosarcoma]]).
**Polyphenotypic tumours.
**[[Rhabdomyosarcoma]].
**[[Neuroblastoma]] (possibly).
*Several other EWS translocations exist.<ref>URL: [http://www.cancerindex.org/geneweb/EWSR1.htm http://www.cancerindex.org/geneweb/EWSR1.htm]. Accessed on: 20 November 2011.</ref>
**ERG,<ref name=omim165080>{{OMIM|165080}}</ref> ETV1, E1AF and FEV.
*Lack of molecular findings does ''not'' exclude Ewing sarcoma.
*Testing:
**A break apart probe for EWS is a common way to look for pathologic change, as it covers almost all variants.
 
==Electron microscopy==
*Primitive cell junctions.
*Clear zone (glycogen lakes).
 
==See also==
*[[Bone]].
*[[Chondro-osseous tumours]].
 
==References==
{{Reflist|2}}


[[Category:Diagnosis]]
[[Category:Diagnosis]]
[[Category:Chondro-osseous tumours]]
Michael
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