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Intra-Abdominal Desmoplastic Small Round Cell Tumor - Immunohistochemical and ultrastructural study -

= Abstract = We report a case of malignant intraabdominal tumor in a 14 years old Korean girl that presented with abdominal pain, distension and palpable mass. Emergency laparotomy revealed bulky peritoneal masses with numerous satellite implanting nodules. Ught microscopically the tumor was characterized by discrete islands of compact, small epithelium-like cells encased in desmoplastic stroma. Immunohistochemically the neoplastic cells expressed vimentin strongly and diffusely and also neuron specific enolase strongly and focally. Ultrastructurally the neoplastic cells showed whorled intermediate filaments, a fair number of mitochondria, dilated rough endoplasmic reticulum, a few fat vacuoles and zonula-adherens type junctions. However there was no evidence of specific differentiation. Histologic, immunohistochemical, and electronmicroscopic observations indicated a primitive malignant neoplasm simultaneously expressing mesenchymal and neural differentiation. Our case did not express any epithelial markers including pancytokeratin, epithelial membrane antigen and CAM 5.2.