Bone
Other tumors of bone
Ewing sarcoma / primitive or peripheral neuroectodermal tumor (PNET)

Author: Nat Pernick, M.D. (see Authors page)

Revised: 20 October 2016, last major update June 2005

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed search: ewing sarcoma [title] bone

Cite this page: Ewing sarcoma / primitive or peripheral neuroectodermal tumor (PNET). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/boneewing.html. Accessed December 6th, 2016.
Definition / General
  • Terms usually used interchangeably; some suggest to call Ewing if undifferentiated or a bone tumor and PNET if neural morphologically or a soft tissue tumor
  • #2 bone sarcoma in children (6% - 10% of childhood primary malignant bone tumors) after osteosarcoma
Clinical Features
  • Usually whites ages 5 - 20 years, variable gender preference
  • May present with pain, fever, weight loss, leukocytosis and increased erythrocyte sedimentation rate mimicking osteomyelitis
  • Sites: marrow of femur, tibia, humerus, fibula, pelvis, ribs, vertebra, mandible, clavicle; may permeate cortex and invade soft tissue
  • 5 year survival: 75%; 50% are cured; metastases to lung, skull, pleura, CNS; 10% - 25% have multiple lesions at presentation
  • Grossing these tumors: first priority is to obtain sufficient formalin fixed tissue for diagnosis; second priority is to obtain 100 mg of viable snap frozen tissue for special studies
Radiology Description
  • Destructive, lytic tumor with reactive periosteal bone resembling onion skin
  • Widening of medullary canal
  • Post treatment Xray: treatment successful if regression of soft tissue mass, reconstitution of cortical pattern
Radiology Images
Images hosted on PathOut server:

Humerus xray - contributed by Dr. Mark R. Wick

Phalanx of foot xray - contributed by Dr. Mark R. Wick

Femur xray - contributed by Dr. Mark R. Wick

Metatarsal MRI - contributed by Dr. Mark R. Wick


Ulna xray - contributed by Dr. Mark R. Wick

Upper end of femur

Destruction of cortex

Subperiosteal defect

Prognostic Factors
  • High stage, direct extension into soft tissue, aneuploidy, metastases, grossly viable tumor post chemotherapy, possibly filigree pattern (bicellular strands of tissue separated by filmy vascular stroma)
Case Reports
Treatment
  • Preoperative chemotherapy, surgery, radiation therapy
Gross Description
  • White, fleshy, ill defined tumor with extensive involvement of medulla and cortex with periosteal elevation
  • May be necrotic or resemble pus
Gross Images
Images hosted on PathOut server:

Contributed by Dr. Mark R. Wick



Images hosted on other servers:

26 year old man with Ewing sarcoma of knee

Micro Description
  • Sheets of small, round, uniform cells 10 - 15 microns (larger than lymphocytes) with scant clear cytoplasm, divided into irregular lobules by fibrous strands
  • Indistinct cell membranes
  • Round nuclei with indentations, small nucleoli
  • May have Homer-Wright rosettes (central fibrillary space) or pseudorosettes (cells arrange themselves around vessels), hemorrhage and necrosis, prominent vasculature, variable mitotic figures
  • May have large pleomorphic cells (Am J Surg Pathol 1980;4:29), organoid pattern, filigree pattern (large areas of perivascular tumor necrosis with “ghost cells”)
  • Little stroma, no spindling
  • May have adamantinoma-like features (Am J Surg Pathol 1999;23:159)
  • Post treatment: marked pleomorphism, tumor giant cells
Micro Images
Images hosted on PathOut server:

Small cell Ewing sarcoma

Large cell Ewing sarcoma

Neuroectodermal tumor

Extends between normal trabeculae


Foot - contributed by Dr. Mark R. Wick

PNET - contributed by Dr. Mark R. Wick

Contributed by Dr. Mark R. Wick


Wilder reticulin stain

CD99 - contributed by Dr. Mark R. Wick

PAS stain - contributed by Dr. Mark R. Wick

PAS stain



Images hosted on other servers:

Quiz case

Univ Pittsburgh Case #103

Xray, MRI, H&E, EM

Xray, CT, H&E, PAS, CD99

Cytology Images
Images hosted on PathOut server:

Touch imprint

Touch prep - contributed by Dr. Mark R. Wick

PNET FNAB - contributed by Dr. Mark R. Wick

PNET lung FNAB - contributed by Dr. Mark R. Wick

Positive Stains
Negative Stains
Molecular / Cytogenetics Description
  • t(11,22)(q24;q12) in 85%; 22q12 is EWS, a transcription factor; 11q24 is FL1
  • EWS / FLI1 is a transactivator of the c-myc promoter
  • t(21;22)(q22;q12) in 5% - 10% - ERG and EWS
Molecular / Cytogenetics Images
Images hosted on PathOut server:

Translocation FISH - contributed by Dr. Mark R. Wick

Electron Microscopy Description
  • Primitive appearance with limited cytoplasmic organelles
  • Glycogen, desmosome associated proteins but no true desmosomes
  • Rare dense core granules
Electron Microscopy Images
Images hosted on PathOut server:

Electron micrograph

Differential Diagnosis
Additional References