Primitive neuroectodermal tumor arising in the colon: report of a case.

Peripheral primitive neuroectodermal tumors (pPNETs) are usually found in the soft tissue of the extremities, paravertebral region, and chest wall. We report a rare case of a pPNET arising in the colon. A 59-year-old man underwent left hemicolectomy for an infiltrative ulcerating tumor, 11 cm long, in the descending colon. Histological examination of the resected specimen revealed small, round cell proliferation with rosette-like structures, and confirmed regional lymph node involvement and peritoneal dissemination near the primary tumor. Immunohistochemically, the tumor cells were positive for synaptophysin and MIC2 (CD 99). ESW-FLI1 chimeric mRNA was detected in the tumor by reverse transcriptase-polymerase chain reaction. The patient underwent resection of recurrence in the retroperitoneum 3 months later, but metastasis rapidly developed and he died of the disease 7 months after his first operation.