Primary Ewing's Sarcoma / Primitive Neuroectodermal (Neuroepithelial)Tumour of the Kidney, ES/PNET, NETK

Clinical features

This is a rare tumour, predominantly of young adults, with a slight male predominance. They show the same t(11;22)(q24;q12) translocation and EWS-FLi-1 gene fusion as seen in extra-renal ES/PNET.

Radiology

Macroscopic appearances

Histopathology

These are poorly differentiated, highly cellular, round cell tumours. Rosette formation is seen: these may be of Flexner-type with a central lumen or of Homer Wright type with a fibrillary core. Cytoplasm is usually scarce but some cases show bubbly glycogen-laden cytoplasm. Nuclei are round to oval and hyperchromatic. Nucleoli are inconspicuous in most cases, but some are more conspicuous, resembling neuroblasts. The arrangement of cells in serpentine tubules and glomeruli, as seen in Wilm's tumour, is not a feature. Some small cell carcinoma–like tumors contained blood vessels deeply encrusted with a basophilic material compatible with DNA (the ``Azzopardi phenomenon'').

Atypical variants include:

• Clear Cell Sarcoma of the Kidney-Like Features : 17/146 cases. These cases showed arborising small blood vessels and clear cytoplasm.

• Malignant Peripheral Nerve Sheath Tumor-like Features : 14/146 cases. These cases showed spindle cells in wavy fascicles. However, Antoni-b areas are lacking. Ganglion-like cells may be seen.

• Rhabdoid Features : 4/146 cases. The rhabdoid cells had eccentric nuclei with owls-eye nucleoli and abundant eosinophilic cytoplasm. : 4/146 cases.

• Epithelioid Features : 14/146 cases. The epithelioid cells form discrete clusters.

• Paraganglioma-like and Sclerosing Features : 13/146 cases. Epithelioid cells separated by arborising vessels form a "zellballen" pattern. Abundant interstitial fibrosis may resemble osteoid but does not calcify. The collagenous stroma may separate tumour nests, resembling desmoplastic small cell tumour.

Immunohistochemistry

	Renal ES/PNET	Wilm's tumour
CD99	65/69 (membranous)2, 11/11 strongly positive1	1/51
Fli-1	5/81	0/101
WT-1	0/101	7/9 (predominantly in the blastemal component) 1
AE1/3	0/22, 2/11(focal)1
Desmin	0/111
chromogranin	3/352
synaptophysin	2/22
NSE	6/72
vimentin	4/52

Ultrastructure

Neurosecretory granules are present.

Differential diagnosis (round cell tumours of the kidney)

• most commonly: blastema-predominant Wilm's tumour: positive for WT-1 but negative for Fli-1.

• lymphoma: often CD99 positive⁴.

• clear cell sarcoma

• small cell carcinoma: may also show neural features such as rosettes. Rare CD99 positivity has been reported³.

• monophasic synovial sarcoma

• metastatic neuroblastoma

• desmoplastic small round cell tumour

Prognosis

As at other sites, this is an aggressive tumour.

References

¹Jimenez, R. E., Folpe, A. L., Lapham, R. L. Primary Ewing's sarcoma/primitive neuroectodermal tumor of the kidney: a clinicopathologic and immunohistochemical analysis of 11 cases. Am J Surg Pathol 2002;26:320-7.

²Parham, D. M., Roloson, G. J., Feely, M., Green, D. M., Bridge, J. A., Beckwith, J. B. Primary malignant neuroepithelial tumors of the kidney: a clinicopathologic analysis of 146 adult and pediatric cases from the National Wilms' Tumor Study Group Pathology Center. 2001;25:133-46.

³Lumadue JA, Askin FB, Perlman EJ. MIC2 analysis of small cell carcinoma. Am J Clin Pathol 1994;102:692–4.

⁴Ramani P, Rampling D, Link M. Immunocytochemical study of 12E7 in small round-cell tumors of childhood: an assessment of its sensitivity and specificity. Histopathology1993;23:557–61.

This page last revised 3.6.2002.

©SMUHT/PW Bishop