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We report the clinicopathologic and cytogenetic findings in an unusual case of primary liposarcoma of bone. A 16-year-old girl presented with a destructive, osteolytic tumor of the proximal humerus. Upon biopsy, the tumor was highly anaplastic and necrotizing and was initially considered to be consistent with osteosarcoma. Following chemotherapy, there was 100% tumor necrosis in the resection specimen. Twentyeight months later, solitary supraclavicular and pulmonary metastases appeared with the morphologic features of pleomorphic liposarcoma. Retrospective review of the bone biopsy showed scattered lipoblasts and no unequivocal malignant osteoid. Ghost-like remnants of necrotic liposarcoma were seen in the resection specimen. Cytogenetic analysis of a metastatic lesion showed complex karyotypic abnormalities. Awareness of the existence of primary bone sarcomas with lipogenic differentiation expands the differential diagnosis of malignant bone tumors including cases in the pediatric population. This is the first report of cytogenetic findings in this tumor.

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.

Rhabdomyosarcoma is one of the most common sarcomas of childhood. It usually arises in the soft tissues but may involve bone by several different mechanisms, includ ing direct extension, metastatic spread, as a component of dedifferentiated chondrosar coma or malignant mesenchymoma, or as a primary tumor. Only nine cases of primary rhabdomyosarcoma of bone have been previously reported, many of them not well documented. The histologic, immunohistochemical, and ultrastructural findings of a primary rhabdomyosarcoma of the femur in a 68-year-old woman are presented. Also discussed are the different aspects of skeletal muscle differentiation in bone tumors and the possible explanation for the rarity of primary skeletal rhabdomyosarcoma. Int J Surg Pathol 1(4):253-260, 1994