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A Case Report of a Spontaneous Gastrointestinal Stromal Tumor (GIST) Occurring in a F344 RatDivision of Pathology, National Institute of Health Sciences, Setagaya-ku, Tokyo 158-8501, Japan Correspondence: Address correspondence to: Dr. M. Shibutani, D.V.M, Ph.D, Division of Pathology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan; e-mail:shibutan{at}nihs.go.jp
We report a case of gastrointestinal stromal tumor (GIST) that developed in a male F344 rat at week 101 of an experiment in a carcinogenicity study. Macroscopically, the primary tumor, which measured 1 cm in diameter, involved the submucosal tissue of the forestomach at the lesser curvature extending to the glandular stomach and esophagus. Histopathologically, the tumor was composed of neoplastic cells with small- to medium-sized spindle-shaped single nuclei and fibrillary cytoplasm lacking distinct cell borders. It invaded extensively into the tunica muscularis and subserosa, further extending to the lamina propria mucosa and serosal surface. A few densely proliferating portions showed a tendency to storiform pattern. Metastatic tumor nodules were found in the liver, spleen, and femur bone marrow, with multiple nodules, up to 1 cm in diameter, apparent in the liver. Immunohistochemically, diffuse, but weak cytoplasmic immunoreactivity for KIT was evident, and most neoplastic cells also exhibited strong immunoreactivity for
Key Words: Gastrointestinal stromal tumor (GIST) • spontaneous occurrence • F344 rat • immunohistochemistry • KIT • interstitial cell of Cajal Abbreviations: GIST, gastrointestinal stromal tumor • SMA, smooth muscle actin
Toxicologic Pathology, Vol. 34, No. 2,
164-167 (2006) This article has been cited by other articles:
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-smooth muscle actin and vimentin. Sparse nuclear S-100-immunoreactive cells were further observed, but none of neoplastic cells were immunoreactive for CD34, caldesmon, desmin, cytokeratin, or synaptophysin. Collectively, these features meet the criteria for a GIST, with limited potential for differentiation to smooth muscle and neural cells. 
