Ewing Sarcoma of Kidney: A Rare Entity

Abstract Primary renal origin of Ewing sarcoma/PNET (primitive neuroectodermal tumor) is a rare entity in the adult population and has an aggressive outcome. The entity was first coined by Arthur Purdy stout in 1918 and recognized under family of small round cell tumor. Radiologically it is difficult to distinguish from primary clear cell carcinoma of kidney from Ewing/PNET. Diagnosis of this requires histopathology, immunohistochemistry (IHC), and cytogenetics studies. A 40-year-old female presented with hematuria and radiology found a mass lower pole of left kidney with extension into renal hilum. Nephrectomy was done for the case and the histopathology diagnosis of small round cell tumor of left kidney was given. Followed by IHC, diagnosis of malignant round cell tumor was suggestive of Ewing sarcoma. Microscopy showed cells with small, round, hyperchromatic nuclei, scant cytoplasm, and inconspicuous nucleoli. Increased mitosis was noted (15/10 high power field). Multiple foci of pseudorosettes, areas of hemorrhage, and necrosis lymphovascular emboli were seen. IHC done outside showed NKX 2-2, synaptophysin positivity, CD99 diffuse membranous positivity, cytokeratin perinuclear dot like positivity, and negative for CD20, CD3, desmin, CD34, S100, and Pax8. Impression of malignant round cell tumor was suggestive of Ewing sarcoma. Ewing sarcoma is one of the rare yet highly aggressive tumors. This should be kept as differential diagnosis in young adults with renal mass, as on radiologically it cannot be differentiated from renal cell carcinoma. Diagnosis of Ewing sarcoma is done using histopathology, IHC, and cytogenetic study. Early diagnosis helps in initiation of surgery, chemotherapy, and radiotherapy and helps in increasing the survival rate.