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Rhabdomyosarcoma

Non-RMS

 

 

Ewing Sarcoma

 

 

PNET

Background: Primitive neuroectodermal tumors (PNET)

Ewing sarcoma (ES):

  • is a type of Primitive NeuroEctodermal Tumor
  • ES family of tumors (ESFT), include ES (Ewing sarcoma) and pPNET
  • are a group of aggressive malignant tumors of childhood and young adults which may arise in bone of soft tissue

ES is predominantly of skeletal origin while pPNET usually presents in soft tissues.

PNETs are a group of small round cell tumors which share the following features:

  • morphological
  • immunohistochemical
  • ultrastructural
  • cytogenetic

They comprise two main groups:

  • Central. A central PNET (cPNET) arises within the central nervous system - medulloblastoma is the prototype.
  • Peripheral. A peripheral PNET (pPNET) refers to a group of tumors including neuroblastoma, peripheral PNET, and Ewing Sarcoma (ES).

 

Cell of origin could possibly be:

  • Pluripotential neural crest cells.
  • Mesenchymal stem cell that differentiates along neural crest lineage.


        

pPNETs

         pPNET by definition shows evidence of neural differentiation either by light microscopy, immunohistochemistry or electron microscopy.

         A range of appearances, depending on the extent of neural differentiation, are apparent in ESFT, from ‘undifferentiated’ Ewing sarcoma to neural differentiation pPNET.

 

 

Immunohistochemistry:

 

Typical Immunohistochemical profile of ES and pPNET:

Immunohistochemistry

Ewing Sarcoma

pPNET

Vimentin

+

+

CD99

+

+

NSE

-

+

Pgp 9.5

-

+

S100

-

+

Chromagranin

-

+

Leu 7

-

+

 

It is impossible to distinguish between members of the Ewing sarcoma family based on staining alone. Ultrastructural and cytogenetic differences are used to further characterize these tumors.

 

Typical ultrastructural findings in ES and pPNET:

Ultrastructure

Ewing sarcoma

pPNET

Cytoplasmic glycogen

+++

+

Adhesion areas

Few

More common

Organelles

rare

More common

Cell processes

-

+

Neurosecretory granules

rare

+

 

Histology shows sheets of small round blue cells:

 

 

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