Abstract
A 13.5kg, 15-year-old male mongrel dog with anemia, anorexia, vomiting and abdominal distension was referred to the Veterinary Medical Center of the Tokyo University. Radiographic and ultrasonographic findings indicated primary splenic tumor. The tumor was located at body of the spleen, which was surgically removed by splenectomy. Histopathological examination of the mass revealed sarcoma type tumor derived from the mesenchymal origin. The patient was in good health after surgery but suddenly showed abdominal distension on the 3 months after. Radiographic findings indicated abdominal neoplasms. The 2nd operation was performed and removed the recurrent mast but suddenly died on the 4th day. Histopathological examination of the tumor was myxosarcoma.