Vet Pathol 28:30-36 (1991) Gastric Stromal Tumors in Two Rhesus Macaques (Macaca mulatta)

Abstract. Two female rhesus monkeys (Macaca mulatta, 10 and 24 years old) developed microcytic anemia and became terminally ill. At necropsy, large gastric masses were present, and, in one case, there were widespread abdominal metastases. Except for slightly atypical patterns, at the light microscopic level, the lesions resembled smooth muscle tumors. Ultrastructurally, however, cells in both tumors resembled primitive mesenchyme, while in one of the tumors, there were some characteristics of Schwann cells. No ultrastructural features of smooth muscle were present in either tumor. Vimentin and S-l 00 were detected immunohistochemically in both tumors. S-IOO staining was more intense in the tumor with ultrastructural features ofSchwann cells. Actin and desmin were not expressed in either gastric tumor, but diffusely stained a uterine tumor that was concomitantly present in one of the rhesus monkeys. The uterine tumor also exhibited typical ultrastructural features ofsmooth muscle. In the past, gastrointestinal stromal tumors in all species were thought to be of smooth muscle origin. Recently in human pathology, this conventional viewpoint has given way to the realization that there is a spectrum of neural crest and mesenchymal tumors. We report two gastric stromal tumors in two rhesus monkeys that histologically resembled smooth muscle tumors but were ofneuroectodermal and primitive mesenchymal origin. Key words: Immunohistochemistry; neoplasia; nonhuman primates; stomach; ultrastructure. developed microcytic anemia, severe arthritis, and was ter