Pleomorphic myofibrosarcoma of the tibia with aneuploid DNA content.

Myofibrosarcomas of the tibia are exceedingly rare, with only one case reported in the literature. We describe DNA ploidy of high-grade myofibrosarcoma of the tibia in correlation with clinicomorphologic and ultrastructural features in a 16-year-old adolescent girl. Radiological studies revealed an expanding osteolytic bone lesion in the metaphysis of proximal tibia. A biopsy was consistent with malignant fibrous histiocytoma. The final diagnosis of myofibrosarcoma was supported by light microscopy and corroborated by electron microscopy and immunohistochemistry findings. The DNA content analysis showed an aneuploid tumor. She developed local recurrence at 6 months after initial treatment with no evidence of lung metastases and 16 months later is alive with persistence of disease. This is the second case reported in the literature with this location. In this case, the high grade correlated with recurrence behavior and aneuploidy DNA content but not with metastases. By ultrastructural analyses, fibronexus and intracellular collagen persisted in high-grade myofibrosarcoma.