Gastric leiomyosarcoma with massive myxoid degeneration. A histochemical and ultrastructural study.

Histochemical and ultrastructural features of a gastric myxoid leiomyosarcoma from a 55-year-old man were examined. At autopsy, the tumor was located mainly in the greater omentum and was directly connected to a coinsized gastric tumor. Multiple hepatic metastases and peritoneal disseminations were noted. Light-microscopically, the tumor was composed of a prominent myxoid stroma and ovoid or rounded tumor cells. The myxoid stroma was stained weakly basophilic with hematoxylin and eosin, and was mainly composed of hyaluronic acid. Tumor cells in the stomach were spindle-shaped and apparently myogenic. Ultrastructurally, the gastric tumor cells showed a loose cohesion with junctional apparatuses, pinocytotic vesicles, basal laminae, and cytoplasmic filaments with focal densities. Tumor cells in the omentum and the liver, however, were poorly differentiated and showed an epithelioid nature in part. This unique leiomyosarcoma is reported with some differential diagnoses from other myxoid sarcomas.