Abstract

Primitive neuroectodermal tumor (PNET) is a small round cell neoplasm that mainly develops in the central nervous system and soft tissue of children. Primary occurrence in the kidney is rare and the identification of immunopositivity for CD99 and t(11;22)(q24;q12) is essential in differential diagnoses. We report two cases of PNET developed in a 21-year-old woman and a 44-year-old man. Resected tumors were composed of sheets of round or ovoid cells with hyperchromatic nuclei and minimal eosinophilic cytoplasm. Rosette formations, more prominent in the first case, were observed. The tumor cells of both cases were diffusely positive for CD99, vimentin, and neuron specific enolase, while they were negative for cytokeratin, desmin, and chromogranin. Synaptophysin was focally expressed only in the first case. The EWS-FLI1 chimeric gene was identified by a reverse transcriptase-polymerase chain reaction in the first case. The first patient is alive with a recurrent tumor two years after the diagnosis, and has received combination chemotherapy. The second patient is alive with no evidence of recurrence or metastasis nineteen months after the diagnosis.