Case of the Week

2020-34 / August 24 (Contributors: Kotaro Takeda and Ann T. Sutton)

A woman in her 20s presented with gross hematuria for over 3 months. MRI identified a 7.2 cm left renal mass. Metastatic disease was excluded based on imaging.

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3 photo(s) Updated on: August 21, 2020

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Quiz

1. What is the correct diagnosis?

a. Nephroblastoma

b. Neuroendocrine carcinoma

c. Ewing sarcoma

d. Lymphoma

e. Rhabdomyosarcoma

2. What is the most common translocation for this disease?

a. t(X;17)

b. t(X;18)

c. t(12;15)

d. t(6;11)

e. t(11;22)

Ewing sarcoma, first described in 1921, is an aggressive malignant neoplasm, usually of bone and soft tissue in children and young adults. Ewing sarcoma and primitive neuro-ectodermal tumors (PNET) are considered the same tumor. Primary Ewing sarcoma of the kidney is very uncommon. The median patient age is 20 to 30 years and the male-to-female ratio is 3:1.

Ewing sarcoma of the kidney usually forms a large renal mass with hemorrhage and necrosis. Microscopically, they have primitive-appearing small round cells with scant cytoplasm and round nuclei, arranged in sheets with a vaguely lobular pattern separated by thin fibrous bands. Rosettes are occasionally seen. The morphology of Ewing sarcoma of the kidney is indistinguishable from those in Ewing sarcoma of other sites. The tumor cells have a strong and diffuse membranous expression of CD99. As many as 90% of Ewing sarcoma of the kidney show the characteristic chromosomal translocation of t(11;22)(q24;q12), leading to the EWSR1-FLI1 fusion gene, and about 5% have t(11;21) with EWSR1-ERG fusion.

The differential diagnosis for this rare malignancy can be broad and includes other "small round blue cell tumors" like blastemal nephroblastoma, rhabdoid tumor, rhabdomyosarcoma, lymphoma, and renal cell carcinoma. Clinical information, morphology, immunohistochemical features and genetical analysis are all required to reach a correct diagnosis.

About GUPS

The Genitourinary Pathology Society (GUPS) was formed with the vision of advancing the care of patients with urologic diseases through enhancements of best practices, research, and education in the subspecialty of Urological Pathology.

GUPS is an official Companion Society of the United States and Canadian Academy of Pathology (USCAP).

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