Microscopic description:

The H&E slides shows tumor cells that are small to medium sized, arranged in sheets and separated by thin fibrous septae. The cells have round nucleus, small round nucleoli and scant cytoplasm. Tumor cells are invading the surrounding perinephric fat.

The diffuse round cell pattern should narrow the differential diagnosis to Ewing sarcoma, Merkel cell carcinoma, small cell carcinoma, embryonal rhabdomyosarcoma and lymphoma.

Immunostains show positive staining for CD99(diffuse), S100 (focal) and synaptophysin. AE1/AE3, WT-2, CAIX, CD3, CD20, CD45, CK 7, CK 20, PAX-8 were read as negative.

Based on the microscopic description and IHC, the tumor shows features compatible with primary Ewing sarcoma of the kidney.

Discussion:

Ewing sarcoma of kidney/Primitive neurectodermal tumor is a very rare malignant tumor of tumor of kidney, usually seen in young adults (mean age between 28 and 34 years) with slight male predominance.

Clinical symptoms include abdominal or flank pain, hematuria and palpable mass. On imaging, these tumors appear as large, ill-defined, heterogenous masses with necrosis and hemorrhage.

Histologically, tumor is composed of sheets/nests of small round cells with finely dispersed chromatin, scant cytoplasm and can show rosette formation. Cells are separated by thin fibrous septae.

Immunohistochemically, tumor cells are positive for CD99 (diffuse). Desmoplastic small round cell tumor show variable positivity for CD 99. Cells are negative for CD 45 (differentiating it from lymphoma), WT-1 (differentiating it from Wilms tumor/nephroblastoma).

Friend leukemia virus integration (FLI-1), a DNA based transcription factor has been found to be overexpressed in majority of cases.

In renal Ewing sarcoma, tumor cells also show diffuse nuclear immunoreactivity for NKX2.2, an important oncogenic transcriptional target of EWSR1/FLI1. NKX2.2 is a valuable marker for Ewing sarcoma, with a sensitivity of 93% and specificity of 89%.

Around 80-95% of the patients show chromosomal translocation t(11;22)(q24;q12) rearrangement whereas 5-20% often display EWS-ETS gene mutation. Hence, molecular testing for EWSR1 gene can help in confirming the diagnosis.

Ewing sarcoma of kidney is typically aggressive and metastasize to lung, bone and liver hence requiring multi-modality treatment. Surgery followed by adjuvant chemotherapy is considered as the main management.

Table of Ewing sarcoma of kidney

Celli R, Cai G. Ewing Sarcoma/Primitive Neuroectodermal Tumor of the Kidney: A Rare and Lethal Entity. Arch Pathol Lab Med. 2016 Mar;140(3):281-5. doi: 10.5858/arpa.2014-0367-RS. PMID: 26927724.

References:

Celli R, Cai G. Ewing Sarcoma/Primitive Neuroectodermal Tumor of the Kidney: A Rare and Lethal Entity. Arch Pathol Lab Med. 2016 Mar;140(3):281-5. doi: 10.5858/arpa.2014-0367-RS. PMID: 26927724

Hakky TS, Gonzalvo AA, Lockhart JL, Rodriguez AR. Primary Ewing sarcoma of the kidney: a symptomatic presentation and review of the literature. Ther Adv Urol. 2013 Jun;5(3):153-9. doi: 10.1177/1756287212471095. PMID: 23730330; PMCID: PMC3655356.

Cheng, L., Xu, Y., Song, H. et al. A rare entity of Primary Ewing sarcoma in kidney. BMC Surg 20, 280 (2020). https://doi.org/10.1186/s12893-020-00948-9

Maria Fernanda Arruda Almeida, Madhavi Patnana, Brinda Rao Korivi, Neda Kalhor, Leonardo Marcal, "Ewing Sarcoma of the Kidney: A Rare Entity", Case Reports in Radiology, vol. 2014, Article ID 283902, 5 pages, 2014. https://doi.org/10.1155/2014/283902

CHOUBEY, S., PIPARA, G., KUMAR, A.. Ewings Sarcoma of the Kidney: A Rare Entity. World Journal of Nephrology and Urology, North America, 6, may. 2017. Available at: . Date accessed: 02 Mar. 2021.

Bartholow, Tanner & Parwani, Anil. (2012). Renal Primitive Neuroectodermal Tumors. Archives of pathology & laboratory medicine. 136. 686-90. 10.5858/arpa.2011-0104-RS.

Yoshida A, Sekine S, Tsuta K, Fukayama M, Furuta K, Tsuda H. NKX2.2 is a useful immunohistochemical marker for Ewing sarcoma. Am J Surg Pathol. 2012 Jul;36(7):993-9. doi: 10.1097/PAS.0b013e31824ee43c. PMID: 22446943.

CASE IMAGES