An unusual leiomyosarcoma of the uterus containing osteoclast-like giant cells.

An unusual variant of a poorly differentiated leiomyosarcoma of the uterus, containing osteoclast-like giant cells, is described. Areas of the resected tumor bore a close resemblance to giant cell tumor of bone. It is postulated that these giant cells, as well as the osteoclast-like giant cells reported in a number of tumors of other tissues, originate from the monocyte/histiocyte group of cells. The diagnosis of leiomyosarcoma was possible only after the tumor had been examined in the electron microscope. The ultrastructural features are consistent with a smooth muscle origin of the neoplasm; the final assessment is based on the relative proportions and frequency of such structures as: bundles of myofilaments with focal densities, marginal densities, pinocytotic vesicles, and an external lamina.