Primary Ewing's Sarcoma of the Kidney Mimicking Renal Cell Carcinoma With Widespread Metastasis: A Case Report and a Brief Review of the Literature.

Ewing's sarcoma family of tumors (ESFTs) are a group of small round cell tumors with common morphological and genetic features, including Ewing's sarcoma of bone, primary extra-skeletal Ewing tumors, extraosseous Ewing sarcoma (EES), and Askin tumors. EES presenting as a primary renal mass is an exceedingly uncommon aggressive tumor with limited reported cases in the literature and often mimics other renal malignancies on imaging. We present a case of a 31-year-old man presenting with left flank pain and abdominal fullness of short duration. Radiological imaging studies showed a large heterogenous mass from the left kidney, confirmed to be Ewing's sarcoma on post-operative histopathological examination (HPE) and immunohistochemistry (IHC) studies. Subsequent follow-up showed extensive metastatic disease. EES of the kidney has a nonspecific presentation and imaging appearance necessitating a multi-disciplinary approach comprising radiological imaging with a high index of suspicion, HPE, IHC, and molecular analysis for the correct diagnosis.