Morphologic and Immunohistochemical Evidence of Continuity Between Different Components of Malignant Mesenchymoma of the Retroperitoneum

Abstract

A malignant mesenchymoma with predominant leiomyosarcomatous component and significant chondrosarcomatous and focal osteosarcomatous elements is presented. Transitional areas with overlapping morphologic and immunohistochemical features were found between the smooth muscle and cartilaginous components. Stains for actin were strongly positive in leiomyosarcoma, and in scattered malignant chondrocytes. Malignant chondrocytes and scattered neoplastic smooth muscle cells were positive for S-100. Both components were strongly positive for p53. Ultrastructurally 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 mesenchymal cell with pluripotential capability. A literature review of retroperitoneal malignant mesenchymomas with similar differentiation is presented.