Peripheral primitive neuroectodermal tumor presenting in the retroperitoneum: a case report with immunohistochemical study.

It is now believed that malignant peripheral primitive neuroectodermal tumor (PNET) form a distinct tumor entity from other malignant small round cell tumors exhibiting neuroectodermal differentiation by morphologic, immunohistochemical or electron microscopic analyses. A 17-year-old Ethiopian boy was found to have a big upper extra osseous retroperitoneal tumor mass not associated with peripheral nerve that had infiltrated the body of the pancreas. Histologic sections from excised biopsy showed neoplastic cells with a high nuclear-cytoplasmic ratio and had an indistinct cytoplasm with numerous Homer-Wright rosettes. Immunohistochemically, isolated tumor cells and the centre of rosettes disclosed strong positivity to neural markers, synaptophysin and chromogranin. To the best of our knowledge, this case report represents the first patient described in Ethiopia.