Gastrointestinal Stromal Tumor Associated with Hypertrophic Osteopathy in a Dog

Background: Gastrointestinal stromal tumor (GIST) is a malignant mesenchymal neoplasm rarely described in the veterinary routine. The aim of this study was to report a case of GIST accompanied by a periosteal reaction, suggestive of hypertrophic osteopathy, in a dog.Case: An 11-year-old male dog had a history of progressive weight loss, difficulty in locomotion, and dyspnea. During clinical care, increased bone volume was observed. Blood samples were collected for a complete blood count and biochemical analysis. The dog also underwent thoracic radiography and abdominal ultrasonography. The test results revealed anemia, leukocytosis, hypocalcemia, hypoalbuminemia, and hypocholesterolemia. The radiographic images of the limbs showed a generalized periosteal reaction, and thoracic radiography indicated changes compatible with mild chronic lung disease. Ultrasonographic findings indicated a neoformation in the intestinal loop of the right mesogastric region and increased volume in the left testicle, both of which were indicative of neoplasia. Therefore, the dog was referred for surgery, wherein the intestinal mass and both testes were removed; the intestinal mass and left testicle were subjected to histopathological diagnosis. The results of the biopsies confirmed that the testicular neoplasm was a seminoma, whereas the intestinal nodule was compatible with GIST, and immunohistochemical analysis was necessary to confirm the diagnosis. On the basis of positive labeling for the antibodies vimentin, desmin, S100, and c-kit, the diagnosis of GIST was confirmed. Therefore, the animal underwent metronomic chemotherapy with 12 mg/m2 cyclophosphamide every 24 h for 3 months, and thereafter every 48 h for 6 months. Moreover, the dog was periodically monitored via imaging (radiography of the anterior and posterior limbs, abdominal ultrasonography, and computed tomography). A few months after the surgical resection of the intestinal nodule, radiography revealed that the periosteal reactions had disappeared, but ultrasonography revealed nonspecific alterations of mild thickening and enlargement of the intestinal loops. Computed tomography revealed two nodular areas of soft-tissue attenuation in the right mesogastric region. Although the possibility of tumor recurrence was raised, the animal’s owner chose only to perform palliative treatment. After 4 months, ultrasonography revealed a neoformation in the right mesogastric region. On July 29, 2018 the animal had a worsening of its clinical condiction, with tumor recurrence by ultrasound exam. The owners didn´t accept returning to the oncologist and made an option for a conservative treatment with tramadol (3 mg/kg/TID), dipirone(25 mg/kg/TID), and vitaminic supplement based on docosahexaenoic acid plus eicosapentaenoic acid (30 mg/kg, once daily) On August, 28, 2018 he was euthanized. The dog’s postsurgical survival time was 15 months.Discussion: The dog described in the present report was large and elderly, both of which are predisposing factors for GIST development. Although non-specific, progressive weight loss may be associated with intestinal neoplasia, owing to the impairment of digestion and nutrient absorption, because a part of the duodenal mucosa was compromised by neoplasia. The difficulty in locomotion, which did not respond to treatment, was attributed to the periosteal reaction confirmed by radiographic exam. This, in turn, was associated with hypertrophic osteopathy secondary to neoplasia, because the condition regressed after the removal of the intestinal nodule. The histopathological findings related to intestinal neoplasia were suggestive of GIST; positive immunoblotting for c-kit, vimentin, S100, and desmin confirmed the diagnosis. Although the veterinarian alerted the owner to the suspicion of recurrence and suggested continuing treatment, the owner chose not to