Primary leiomyosarcoma of the bone and its comparison with fibrosarcoma.

Two cases of primary leiomyosarcoma of the bone are recorded, one in the distal fibula of a 66-year-old man, the other in the proximal tibia of a 61-year-old woman. The cytological, histological, and ultrastructural features of leiomyosarcoma of bone are described and compared with those of fibrosarcoma. These features are sufficiently characteristic to enable a confident diagnostic distinction between leiomyosarcoma and fibrosarcoma. Nevertheless, certain basic similarities exist between these two tumors, manifested at the ultrastructural level by the presence of myofilaments in fibrosarcoma; it would seem that the observed differences relate to the degree of development of the myofilamentous structures. It is postulated that primary leiomyosarcoma of the bone need not necessarily always arise from the media of blood vessels; it might also conceivably develop through advanced myogenic metaplasia of a sarcoma originating from fibroblastic tissue.