Kidney tumor
Other tumors
Ewing sarcoma / primitive neuroectodermal tumor (PNET)

Topic Completed: 1 June 2012

Minor changes: 27 September 2019

Copyright: 2003-2019,, Inc.

PubMed Search: "Ewing sarcoma" "Primitive Neuroectodermal Tumor" (PNET) kidney

Sean R. Williamson, M.D.
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Cite this page: Williamson SR. Ewing sarcoma / primitive neuroectodermal tumor (PNET). website. Accessed October 20th, 2020.
  • Rare; median age 18 years, range 0 - 72 years
Clinical features
  • Abdominal / flank pain or hematuria; usually stage 3 or 4
  • Highly aggressive with rapid death in many cases within 1 year; metastases to lung and pleura; also bone and liver (Am J Surg Pathol 2001;25:133)
  • May recur locally
Radiology images

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CT and MRI

Case reports
  • Surgery, early and aggressive chemotherapy
Gross description
  • Mean 12 cm, often renal medulla or pelvis, hemorrhage and necrosis common, may have cystic change
Gross images

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Irregular fleshy necrotic mass

Microscopic (histologic) description
  • Vaguely lobular growth of highly cellular, round to oval, poorly differentiated cells with minimal to modest pale staining cytoplasm and hyperchromatic nuclei
  • May have bubbly to clear cytoplasm with light and dark round cells, rosettes (in well differentiated tumors) with central solid eosinophilic core containing neurofibrillary material (Homer-Wright rosettes)
  • Neuropil common; rarely has central lumen (Flexner-Wintersteiner rosettes)
  • Also occasional spindle cells (MPNST-like), ganglion cells, clear cell sarcoma-like foci, rhabdoid cells, epithelial cells, organoid foci, adenomatous hyperplasia of Bowman capsule epithelium
  • No tubules or glomeruloid formations as seen in Wilms tumor
  • Azzopardi phenomenon: blood vessels deeply encrusted with basophilic material consistent with DNA; associated with small cell carcinoma
Microscopic (histologic) images

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Cohesive lobules and rosettes

11 year old boy

Vimentin, NSE, CD99 / MIC2

Positive stains
Negative stains
Electron microscopy description
  • Neurosecretory granules
Molecular / cytogenetics description
  • 90% have EWS / FLI1 fusion product by RT-PCR due to t(11;22)(q24/q22;q12)
Differential diagnosis
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