Pathology of Extraskeletal Ewing's Sarcoma /Peripheral Primitive Neuroectodermal Tumour
Ewing sarcoma family
of tumours includes Ewing sarcoma, peripheral primitive neuroectodermal
tumor, neuroepithelioma, atypical Ewing sarcoma, and Askin tumour.
Peripheral primitive neuroectodermal tumours are characterized by chromosomal translocation t(11;22)(q24;q12) in almost 90% cases.
Ewing sarcoma and the peripheral primitive neuroectodermal tumor were both found to contain the same reciprocal translocation between chromosomes 11 and 22, t(11;22).
Both lesions have similar patterns of biochemical and oncogene expression.
The tumour is common between 10 and 30 years.
Usually occurs in deep soft tissue and rarely involves dermis and subcutis.
The common sites include paravertebral and intercostal regions as well as on the lower limbs. Rarely pelvic and hip regions are involved.
Tumour located on the chest wall (may involve ribs, pleura and lung) is referred to as Askin tumour.
The tumour presents as a rapidly enlarging, pale, soft mass with extensive necrosis. One third of the cases are painful.
The tumour cells are arranged in a trabecular or lobular growth pattern. A prominent vascular network is present in the backround.
The microscopic features depends on the degree of neuroectodermal differentiation.
Malignant primitive neuroectodermal tumours (peripheral neuroepithelioma)- well differentiated end of the spectrum.
The tumour cells show eosinophilic cytoplasm,coarse chromatin and prominent nucleoli.
Homer Wright rosette containing central core of neurofibrillary material.
Flexner-Wintersteiner rosette containing central lumen.
PAS positivity is present in about 40% of cases.
A peripheral neuroepithelioma must demonstrate positivity with at least two neural markers.
Extraskeletal Ewing's sarcoma- Poorly differentiated end of the spectrum.
The tumour cells show scanty, pale, cytoplasm, fine dusty chromatin and inconspicuous nucleoli.
The cells contain glycogen. PAS positivity is prominent.
Immunohistochemistry shows characteristic positivity with the neural markers.
FLI-1 has been described to be a useful marker for Ewing sarcoma.
The tumour cells show diffuse membrane positivity positivity with CD99 antigen (product of the MIC2 gene).
The tumour cells are usually positive for neuron-specific enolase, PGP9.5, neurofilament, Leu-7 and synaptophysin.
Note: About 10% cases of PNET may demonstrate dot like positivity with cytokeratin.
PNET and Ewing's sarcoma are immunopositive to vimentin.
Protocol for the examination of specimens from pediatric and adult patients with osseous and extraosseous ewing sarcoma family of tumors, including peripheral primitive neuroectodermal tumor and ewing sarcoma.
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