A 13-year-old spayed mixed-breed dog was diagnosed with a gastrointestinal
stromal tumor (GIST) after histopathological examination of an abdominal mass. Five months
after surgical resection of the tumor, we detected the recurrence of GIST with multiple
disseminated abdominal lesions. A sequence analysis of cDNA obtained from a biopsy of the
recurrent tumors revealed a mutation within exon 9 of the c-kit gene
(1523A>T, Asn508Ile), which has been shown to cause ligand-independent
phosphorylation of the KIT protein in GISTs and canine mast cell tumors (MCTs). Upon
detection of the recurrent tumors, we initiated treatment with imatinib mesylate (10
mg/kg, q 24 hr). After 2 months, the dog achieved complete remission. Our findings
indicate that canine GIST, and possibly MCT, may be responsive to molecular-targeted
therapy.
A 5-year-old castrated Japanese domestic cat was presented with persistent
vomiting. Ultrasound examinations revealed many masses only in the liver, and the fine
needle aspiration was performed. Cytologically, polygonal or oval shaped tumor cells
forming rosette and cord-like patterns were demonstrated, and then, the hepatic lesions
were diagnosed as neuroendocrine carcinoma tentatively. The cat died one month after
admission and was necropsied. Histopathologically, the tumor cells of the hepatic mass
were arranged in typical rosette and cord-like structures. They were considerably uniform
in size with hyperchromatic round nuclei and eosinophilic cytoplasm. Most of tumor cells
were immunopositive for chromogranin A, and some were positive for gastrin. The findings
indicate the possibility that the present case was a gastrin-producing neuroendocrine
carcinoma.
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