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Kidney tumor - adult malignancies

Other neoplasms – adult or adult/child

Ewing’s sarcoma / Primitive Neuroectodermal Tumor (PNET)

Reviewers: Sean Williamson, M.D. (see Reviewers page)
Revised: 11 January 2013, last major update June 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.


● Rare; median age 18 years, range 0-72 years

Clinical description

● 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


● Surgery, early and aggressive chemotherapy

Case reports

● 11 year old boy (Can Urol Assoc J 2010;4:E158)
● 17 year old girl (Am J Surg Pathol 1997;21:354)
● 19 year old man (Arch Esp Urol 2007;60(3))
● 22 year old man with abdominal mass (Arch Pathol Lab Med 1999;123:541)
● 32 year old man with spontaneously ruptured tumor (Int Urol Nephrol 2007;39:393)
● 56 year old woman (Am J Surg Pathol 1997;21:461)
● 3 cases (Hum Pathol 1997;28:767)

Radiologic images

CT and MRI

Gross description

● Mean 12 cm, often renal medulla or pelvis, hemorrhage and necrosis common, may have cystic change

Gross images

Irregular fleshy necrotic mass

Micro 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’s 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

Micro images

Prominent rosettes

Sheet-like growth of primitive round cells

Cohesive lobules, rosettes, and perivascular condensation of tumor cells

Vascular invasion

11 year old boy

Vimentin, NSE, CD99/MIC2

Virtual slides

Various images

Positive stains

● CD99 (membranous staining), FLI1, PAS+ diastase sensitive (glycogen), vimentin, neuron-specific enolase
● Note: CD99 negative cases are usually fusion protein negative

Negative stains

● Cytokeratin (usually), desmin, WT1, GFAP, PAX2 (Am J Surg Pathol 2011;35:1186)
● Note: reliance on immunohistochemistry as sole means of ancillary diagnosis can lead to confusing results - molecular testing is recommended (Hum Pathol 2007;38:205)

Electron microscopy description

● Neurosecretory granules

Molecular description

● 90% have EWS/FLI1 fusion product by RT-PCR due to t(11;22)(q24/q22;q12)

Differential diagnosis

Clear cell sarcoma of kidney: young children, nests of cells separated by vascularized stroma, CD99-, FLI1-, different cytogenetics
Desmoplastic round cell tumor: prominent desmoplastic stroma, WT1+, different translocation also involving EWS t(11;22)
Monophasic synovial sarcoma: fascicular pattern, no rosettes or neuroendocrine features, often hemangiopericytoma-like vascular pattern, different translocation
Neuroblastoma: usually young children, FLI1-, different cytogenetics
Small cell carcinoma: older patients, molding, no light/clear cytoplasm, no rosettes, keratin+, FLI1-, different cytogenetics
Wilms tumor: usually younger patients, triphasic, WT1+, CD99-, FLI1- (Am J Surg Pathol 2002;26:320)

End of Kidney tumor - adult malignancies > Adult renal cell carcinoma > Ewing’s sarcoma / Primitive Neuroectodermal Tumor (PNET)

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