Ewing Sarcoma of the Kidney: A Rare Entity

Ewing sarcoma and primitive peripheral neuroectodermal tumor (PNET) are high-grade malignant tumors typically found in children and adolescents. These tumors belong to the family of small round cell tumors and are of neuroectodermal origin. Primary Ewing sarcoma of the kidney is rare and because of that is an infrequent differential diagnosis in urologic malignancies. Renal PNET mostly presents with nonspecific symptoms such as hematuria and abdominal pain. The imaging findings are uncharacteristic. The diagnosis is based on the histology, immunohistochemistry, and molecular pathologic findings. Once PNET has been diagnosed, multimodal treatment is indicated. Despite all treatment options, the prognosis of those with metastatic disease is poor. 1. Introduction Ewing sarcoma and primitive peripheral neuroectodermal tumor (PNET) were originally described as two distinct pathologic entities, although both share common stem-cell precursor and unique chromosomal abnormality. Because of their similar histologic and cytogenetic characteristics, these tumors are now considered part of a spectrum of neoplastic diseases now known as Ewing’s sarcoma family tumors (ESFT), which also includes other malignancies [1–3]. The ESFT are most common in bone. Extraskeletal ESFT are less common and can affect the skin, soft tissue, or viscera [4, 5]. Renal primary sarcomas are a rare group of renal tumors. Ewing sarcoma/PNET of the kidney is distinctly rare, with more than 100 cases reported globally. Among these, leiomyosarcoma is the most common (40–60%) followed by liposarcoma (10–15%) [2, 3]. 2. Case Report A 19-year-old man presented with sudden sharp right flank pain, accompanied by low-grade fevers and vomiting. He had no other significant medical history and denied any episodes of gross hematuria. Due to worsening of the symptoms, an abdominal ultrasound was performed, which showed an infiltrative mass in the upper pole of the right kidney, invading the right liver, concerning for malignancy (Figure 1). A staging CT scan of the abdomen was then performed revealing a right upper pole renal infiltrative mass, invading the inferior aspect of the right lobe of the liver (Figures 2 and 3). The CT scan of the chest revealed a 7？mm left upper lobe nodule as well as tiny punctate nodules in the right lower lobe, suspicious for metastatic disease (Figures 4(a) and 4(b)). Biopsy of the kidney mass revealed Ewing sarcoma/primitive neuroectodermal tumor (Figure 5). Diagnosis was confirmed by fluorescence in situ hybridization (FISH) technique, which showed translocations