Cytological characterization and histogenesis of Ewing's sarcoma.

In addition to a light-microscopical and histochemical investigation of primary and metastic lesions in 27 cases of Ewing's sarcoma, biopsy materials from the primary bone lesions of 7 patients with this neoplasm were examined histochemically, enzyme-cytochemically and electron microscopically to elucidate the histogenesis and nature of the neoplasm. Ultrastructural observation has revealed that besides intracytoplasmic and extracellular deposition of glycogen the tumor cells possess several cytological features characterized by intracytoplasmic microfilaments of varying thickness up to 80 A, occasional appearance of dense patches, fat droplets, desmosomal connections and reminiscent attachment bodies. The tumor cells are mostly round, oval or polygonal in shape, but spindle or elongated cells are intermingled and occasionally contain well-developed rough endoplasmic reticulum, resembling pericytes or fibroblasts. In the intercellular spaces amongst the tumor cells, varying amounts of variable-shaped amorphous materials are found, which are compatible with acid mucopolysaccharides and glycoproteins histochemically verified. These findings may suggest that Ewing's sarcoma is a highly malignant neoplasm originating from a transitional cell developed from pericytes to vascular smooth muscle cells in the bone marrow.