ABSTRACT
Most submucosal tumors of the stomach are of mesenchymal origin. According to the advances of immunohistochemical staining and electron microscopy, spindle cell tumors which were considered as leiomyoma or leiomyosarcoma appeared to be heterogeneous group; from smooth muscle cell, neural, bidirectionally differentiated cells of smooth muscle cell and neural cell, or immature mesenchymal cell. Therefore, the gastrointestinal mesenchymal tumors are referred to as gastrointestinal stromal tumors. The biologic behavior of gastrointestinal stromal tumors is difficult to predict, except benign leiomyoma and schwannoma. Recently, we experienced a case of 5 cm-diameter submucosal tumor with a central ulcer on body of the stomach, endoscopically. The tumor was a well cir- cumscribed submucosal mass located in the midbody along greater curvature. Micros- copically, the tumor was composed of fasciculating bundles of spindle cells with benign nuclear atypia and peripheral lymphoid cell cuffing. The tumor cells revealed a diffuse strong immunoreactivity to S-100 protein and vimentin, but were negative to desmin and smooth muscle actin. Ultrastructurally, many tumor cells showed a number of thin elon-gated and interdigitating dendritic-like cell processes, distinct uniform basal laminae, frequent cellular attachments and microfilaments. The findings supported the schwannian nature of the tumor.