Case 8 -

Primitive Neuroectodermal Tumor (Ewing Sarcoma) of the Kidney John N Eble, M.D. Holger Moch, M.D.

Case history: 30-year-old woman presented with persistent abdominal pain. A large mass was palpable in the right side of the abdomen extending into the pelvis. Computerized tomography showed an 8 x 7 x 6 cm right renal tumor with regional lymph node enlargement and multiple lung and skeletal metastases. The patient underwent tumor debulking through nephrectomy. After radiotherapy and high-dosed chemotherapy the patient is without evidence of recurrent disease 28 months after therapy. Macroscopic findings: The mass measured in excess of 12 cm in diameter with replacement of the kidney. Cross-sectional features included a gray to tan surface with areas of hemorrhage and necroses. A pseudocapsule was present. Diagnosis: Primitive neuroectodermal tumor (Ewing sarcoma) of the kidney Primitive neuroectodermal tumors (PNET) are highly aggressive neoplasms occurring typically in children and young adults. More than 20 cases have been reported in the kidney. The diagnosis of renal PNET must be considered in young patients with advanced disease at presentation. PNETs consist of nests and sheets of loosely cohesive cells with wide bands of geographic tumor necrosis with perivascular preservation of viable tumor cells. Mitotic figures are numerous. Entrapment of individual nephrons or renal tubules is common. The pathological differential diagnosis of malignant small round cell tumors of the kidney includes monophasic Wilm's tumor, carcinoid, clear cell sarcoma of the kidney (CCSK), primitive rhabdomyosarcoma, neuroblastoma, lymphoma and even the small cell variant of osteosarcoma. Differentiation of PNET from other members of this group is facilitated by immunohistochemical techniques. Antibodies against the MIC2 gene product, such as 12E7, HBA71 (CD99), and 013 may be of diagnostic help because they stain tumors of the Ewing's family. However, absence of CD99 expression does not exclude PNET. Molecular detection of the specific fusion transcripts is an additional tool in the diagnosis of the Ewing's/PNET tumor family. Molecular detection of the specific EWS/FLI-1 translocation may be of diagnostic help especially in CD99-negative tumors. Outcome of PNET depends upon the localization and staging of the tumor, age of the patient, histologic classification, extent of surgical resection and time to treatment. Combination of debulking, high-doses chemotherapy and radiotherapy has shown good results in patients with renal PNETs with metastatic disease at presentation. Therefore, exact diagnosis of PNET has important clinical consequences. References: Rodriguez-Galindo C., et al. Is primitive neuroectodermal tumor of the kidney a distinct entity? Cancer 79: 2243-50, 1997. Marley EF, et al. Primitive neuroectodermal tumor of the kidney--another enigma: a pathologic, immunohistochemical, and molecular diagnostic study. Am J Surg Pathol 21: 354-9, 1997. Jimenez RE, et al. Primary Ewing's Sarcoma/Primitive Neuroectodermal Tumor of the Kidney: A Clinicopathologic and Immunohistochemical Analysis of 11 Cases. Am J Surg Pathol 26: 320-7, 2002 Quezado M, Benjamin DR and Tsokos M. EWS/FLI-1 fusion transcripts in three peripheral primitive neuroectodermal tumors of the kidney. Hum Pathol 28: 767-71, 1997. Casella R, et al. Metastatic primitive neuroectodermal tumor of the kidney in adults. Eur Urol. 39: 613-617, 2001