Ewing's sarcoma, extraskeletal and of bone. Case report with ultrastructural analysis.

Ewing's sarcoma is considered a primary malignant tumor of bone. Histologically, it is characterized by small round cells with poorly delineated borders. Ultrastructural studies reveal large amounts of glycogen aggregated in the undifferentiated cytoplasm of the tumor cells which show variable amount of organelles. The cell membrane shows desmosomes in some cases but not in others. Intercellular argentophylic fibers are by and large absent. In a survey of human sarcomas for the possible presence of viral agents, a sarcoma has been encountered in a 15 year old male originating in the area of the posterior bladder wall and prostate that satisfies morphologic criteria for the diagnosis of Ewing's sarcoma but is extraskeletal in origin. Histology and ultrastructure as well as tissue cultural characteristics of this tumor were studied in comparison with a second patient (age 14) with Ewing's sarcoma originating in the right clavicle. None of the two tumors yielded virus particles in culture.