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Ten cases of extrauterine malignant mixed mesodermal tumors (MMMTs), nine ovarian, and one pelvic, are presented. One patient had a purely epithelial primary ovarian tumor and MMMT in her recurrent tumors. All the other patients had MMMT in their primary and recurrent tumors. Eight patients had heterologous MMMT including cartilage, striated muscle, and adipose tissue in one case. Two patients had homologous MMMT. All cases presented with metastases involving abdominal organs that were either MMMT or epithelial neoplasms and MMMT. Five patients had recurrent tumors, one extensively involving the spleen. In all recurrent tumors, the mesenchymal components were considerably more abundant than in the primary tumors. Immunohistologic studies of intermediate filaments were performed in seven cases, revealing cytokeratin-positive epithelial structures, vimentin-positive mesenchymal (including cartilaginous) structures, as well as coexpression of cytokeratin and vimentin in anaplastic and giant tumor cells in some cases. Some anaplastic spindle cells, which on routine stains were suggestive of stromal cells, stained positive for cytokeratin, thus identifying their epithelial nature. Desmin staining performed in five cases showed positive staining of rhabdomyoblasts in only one case. Myoglobin staining performed in seven cases was positive in four. The histogenesis from primitive müllerian structures and the natural history of these uncommon neoplasms are discussed in light of the pathological and immunohistochemical data presented.