Ultrastructural Study on the Histogenesis of Alveolar Soft Part Sarcoma

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The smooth tubular structures associated with plasmalemmal invaginations were made an ultrastructural search for in 6 alveolar soft part sarcomas to known whether the tumor s usually contained them or not. Two different smooth tubular structures were identified : the aggregated type and the dispersed one. The former had marked aggregates of many elongated smooth tubules without ribosomes close to plasmalemma whereas the latter showed inconspicuous bundles of a few smooth tubules scattered in the cytoplasm. The common components of both types were smooth tubules. Therefore, it is likely that both types had the same origin although there were some differences in number, appearance, and distribution between the types. The smooth tubules of both types were classified into three different subtypes on the basis of inclusive materials in the lumen. A plasmalemmal continuity of smooth tubules in both types was found in 3 cases after intensive observation and using a plasmalemmal tracer-method, suggesting that the tubular structures originated from plasmalemma. Since the tubular structures were found in all 6 cases, the tumors might usually have the tubular structures. The establishment of types and subtypes was helpful to identify the structures in the tumors. It has remained unclear whether the structures are the remnants ot T-tubules ornot.