Hypoglycemia associated with disseminated metastatic tonsillar squamous cell carcinoma producing insulin‐like growth factor‐I in a Pomeranian dog

A 13-year-old spayed female Pomeranian dog was presented for persistent, severe hypoglycemia (37 mg/dL; reference interval [RI] 75-128 mg/dL). Progressive nonregenerative anemia (hematocrit 23.3%-15.9%; RI 37.0%-55.0%) and severe thrombocytopenia (36 000/mu L; RI 200-500 000/mu L) were also noted. The serum insulin concentration was low (0.24 ng/mL; RI 0.302-1.277 ng/mL). Computed tomography revealed multiple splenic nodules (1-6 mm in diameter) and several hepatic nodules (7.6, 12 mm in diameter). Ultrasound-guided fine-needle aspiration of the splenic and hepatic nodules revealed low numbers of epithelial cells with mild cellular atypia, suggestive of a metastatic epithelial tumor, but the primary site was unknown at that time. On careful oral examination under general anesthesia, an enlarged right tonsil was noted grossly, and histopathologic examination of the tonsil diagnosed squamous cell carcinoma. Bone marrow aspirates and biopsies of the splenic and hepatic nodules were performed; all samples were diagnosed as metastatic carcinoma on histopathologic examination. No nodules were present in the pancreas, despite careful palpation during exploratory laparotomy. On immunohistochemistry, the neoplastic cells were positive for cytokeratin AE1/3 and insulin-like growth factor (IGF)-I but were negative for chromogranin A, PGP9.5, insulin, and inconclusive for IGF-II. This is the first report of a primary IGF-I-producing squamous cell carcinoma in the tonsil of a dog with metastases to bone marrow, liver, and spleen, resulting in hypoglycemia.