Soft tissue tumors - Extraskeletal Ewing sarcoma / PNET

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Soft tissue tumors
Extraskeletal bone tumors
Extraskeletal Ewing sarcoma / PNET

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 10 March 2013, last major update November 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

General
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Rare soft tissue tumor, morphologically indistinguishable from Ewing sarcoma of bone, may represent extension of bone tumor into soft tissue
Usually age 30 or less, occasionally age 50+, usually male preponderance
Often chest wall, lower extremities, paravertebral region; also pelvis, hip region, retroperitoneum, upper extremities (Cancer 2011;117:3027)
Aggressive; common metastases to lung, bones

Case reports
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29 year old man with neck tumor exhibiting focal squamous differentiation (Am J Surg Pathol 2008;32:1742)
35 year old woman with abdominal wall mass (Cancer Imaging 2008;8:156)
77 year old woman with inguinal mass (Arch Pathol Lab Med 2001;125:1358)

Gross images
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Knee

Micro description
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Small round/oval cells with scanty cytoplasm containing glycogen
Peritheliomatous pattern (concentration around blood vessels)
Usually more neuroepithelial features than similar bone tumors

Micro images
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Inguinal mass

Various images

Positive stains
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Glycogen, vimentin, CD99 / O13 / mic2, S100, keratin (20%) (Am J Surg Pathol 2000;24:1657)

Negative stains
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CK7, CK19 (usually, Am J Surg Pathol 2000;24:1174)

Electron microscopy description
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Primitive cells, abundant cytoplasmic glycogen, poorly developed cell junctions, no neural features

Molecular / cytogenetics description
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t(11;22)(q24;q12) fusion transcript by RT-PCR of FLI1-EWS genes
t(21;22)(q12q12) of ERG-EWS genes
t(7;22)(p22;q12) of ETV1-EWS genes
t(17;22)(q12;q12) of E1AF-EWS genes
t(2;22)(q33;q12) of FEV-EWS genes
t(4;22)(q31;q12) (Mod Pathol 2011;24:333)

Molecular / cytogenetics images
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t(4;22)(q31;q12)

Differential diagnosis
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End of Soft tissue tumors > Extraskeletal bone tumors > Extraskeletal Ewing sarcoma / PNET

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