Primary stromal tumor of the omentum: Report of a case.

We report the case of a primary extragastrointestinal stromal tumor (EGIST) found in the omentum of a 65-year-old woman. The resected specimen, which measured 6 cm at its largest point, consisted of an outer solid part and inner uniloculated cysts. Microscopically, the tumor was characterized by interlacing bundles of elongated spindle cells, with the nuclei showing a focal palisading pattern; however, skenoid fibers were not observed anywhere and mitoses were absent. Immunohistochemically, the tumor was negative for smooth-muscle actin, desmin, and S-100 protein, but it was positive for CD117 and CD34. The microscopic features were consistent with a gastrointestinal stromal tumor.