Gastric fibromyxoma, a distinct entity of pure fibroblastic tumor--an ultrastructural study.

A rare case of fibromyxoma arising in the stomach of a 78-year-old male is presented. A well-defined, encapsulated tumor measuring 27x17x8 cm showed a lobular growth in the submucosa and muscularis propria, with no association with the propria mucosa. Histologically, the tumor was characterized by a diffuse, widely spaced proliferation of small spindle, stellate and round cells with dendritic outlines with fibromyxoid stroma. Neither cellular atypia nor mitotic figures were observed. Immunohistochemically, the tumor was positive for vimentin and CD34 but negative for CD117, alpha-smooth muscle actin, muscle actin, desmin and S-100 protein. Ultrastructurally, the tumor cells had irregularly shaped nuclei and cytoplasm containing moderate amounts of mitochondria, rough endoplasmic reticulum, subplasmalemmal densities, and short interdigitating processes. These findings indicated the fibroblastic nature of the tumor. The patient was well without recurrence 20 months after surgery. It is important to recognize that gastric fibromyxoma is a distinct entity and to include it in the differential diagnosis of gastric mesenchymal tumors, as the tumors show a different clinical behavior and as limited surgery with local excision is possible.