MORPHOLOGIC AND IMMUNOHISTOCHEMICAL EVIDENCE OF CONTINUITY BETWEEN DIFFERENT COMPONENTS OF MALIGNANT MESENCHYMOMA OF THE RETROPERITONEUM - A CASE-REPORT

A malignant mesenchymoma with predominant leiomyosarcomatous component and significant chondrosarcomatous and focal osteosarcomatous element s is presented. Transitional areas with overlapping morphologic and im munohistochemical features were found between the smooth muscle and ca rtilaginous components. Stains for actin were strongly positive in lei omyosarcoma, and in scattered malignant chondrocytes. Malignant chondr ocytes and scattered neoplastic smooth muscle cells were positive for S-100. Both components were strongly positive for p53. Ultrastructural ly there were calcified particles in the matrix of both chondrosarcoma and leiomyosarcoma. These findings support the concept that malignant mesenchymoma results from divergent differentiation of primitive mese nchymal cell with pluripotential capability. A literature review of re troperitoneal malignant mesenchymomas with similar differentiation is presented.