Gastric Neuroendocrine Carcinomas in Bearded Dragons (Pogona vitticeps)

Abstract

This article describes a newly recognized highly malignant neoplastic entity in young bearded dragons ( Pogona vitticeps), gastric neuroendocrine carcinomas, which readily metastasize. Ten bearded dragons with histories of anorexia (8), vomiting (3), hyperglycemia (2), and anemia (3) were included in this study. All animals had neoplastic masses in their stomach, with metastasis to the liver. Microscopically, 6 of these neuroendocrine carcinomas were well-differentiated and 4 were poorly differentiated. For further characterization, immunohistochemistry for protein gene product 9.5, neuron-specific enolase, endorphin, chromogranins A and B, synaptophysin, somatostatin, insulin, glucagon, gastrin, pancreatic polypeptide, and vasoactive intestinal peptide was performed on 5 animals. Because only immunolabeling for somatostatin was consistently observed in all neoplasms, a diagnosis of somatostatinoma was made for these 5 bearded dragons. Some neoplasms also exhibited multihormonal expression. Electron microscopy performed on 1 tumor confirmed the presence of neuroendocrine granules within neoplastic cells. Gastric neuroendocrine carcinomas, and specifically somatostatinomas, have not been previously reported in bearded dragons, or other reptiles, and may be underdiagnosed due to inconsistent, ambiguous clinical signs. In humans, pancreatic somatostatinomas are associated with a syndrome of hypersomatostatinemia, which includes hyperglycemia, weight loss, and anemia, as observed in some of these bearded dragons. Somatostatinomas in humans are commonly associated with neurofibromatosis type 1 (Von Recklinghausen's disease), caused by a mutation in the tumor suppressor gene NF1, which results in decreased expression of neurofibromin. In all 5 animals examined, neoplasms exhibited decreased neurofibromin expression compared with control tissues, suggesting that decreased functional neurofibromin may play a role in the pathogenesis of somatostatinomas in bearded dragons.