Primary leiomyosarcoma of bone.

We describe a primary leiomyosarcoma arising in the proximal part of the right tibia of a 65-year-old man. The diagnosis was confirmed by both histochemical and electron microscopical studies. Ultrastructural examination revealed two different neoplastic cell populations. One, the type 1 cell, resembled typical mature smooth muscle cells, whereas the type 2 cells were smaller, more pleomorphic, and contained thick myofilaments in addition to the characteristic thin actin-like filaments. The tumor most likely arose from vascular smooth muscle cells, although origin from perivascular, multipotential, mesenchymal cells cannot be ruled out. Prognosis of reported cases appears to be poor if they are treated by inadequate surgical excision and irradiation but is more promising if wide excision or major amputation is performed.