Primitive neuroectodermal tumor (PNET) in the differential diagnosis of malignant kidney tumors.

Primitive neuroectodermal tumors (PNETs) of the kidney, a rare neoplastic disease of high malignancy with a tendency towards early metastasis, affect young adults (26-30 years) irrespective of the gender. Differential diagnosis from other renal tumors is very important for an effective therapy. Herein, we report on a 24-year-old male patient with a renal tumor consisting of small, round cells, and summarize the diagnostic procedures that establish the diagnosis of PNET. Light microscopy revealed not only areas containing small, round cells forming rosettes and pseudorosettes, but also areas containing spindle cells. Expression of CD 99 in combination with neural markers, such as NSE, was detected by immunohistochemistry, and further evidence of neural differentiation was provided by electron microscopy. Image cytometry revealed a peridiploid DNA-stemline. A reciprocal translocation of the chromosomes 11 and 22 [t(11;22)(q24;q12)] with expression of a EWS/FLI-1 fusion transcript was demonstrated by molecular pathology. Using these methods, the diagnosis of PNET was firmly established, and the tumor was treated by surgical resection and subsequent adjuvant chemotherapy. Eighteen months after therapy, the patient is in excellent health condition without any evidence of tumor recurrence.