RESUMEN
The Calcitonin-negative neuroendocrine tumor of the thyroid (CNNET) or "nonmedullary" in humans is a rare tumor that arises primarily in the thyroid gland and may be mistaken for medullary thyroid carcinoma; it is characterized by the immunohistochemical (IHC) expression of neuroendocrine markers and the absence of expression for calcitonin. An Argentine dogo bitch showed a solid, compact thyroid tumor, which was IHC negative for the expression of calcitonin, carcinoembryonic antigen, thyroglobulin and S100 protein, and positive for synaptophysin and cytokeratin AE1-AE3. The Ki-67 proliferation index was low. We cite this case not only because it is the first case report of calcitonin-negative primary neuroendocrine tumor of the thyroid in dogs but also because we want to highlight the diagnostic importance of IHC in this regard.
RESUMEN
Human multiple endocrine neoplasia subtype 2A (MEN 2A) is characterized by medullary thyroid carcinoma, pheochromocytoma and parathyroid hyperplasia or adenoma in the same individual. In this report, a case of a female Rottweiler with medullary thyroid carcinoma, bilateral pheochromocytoma and parathyroid adenoma was described. Clinical manifestations of muscle weakness, polydipsia, polyuria, diarrhea and weight loss were observed. Two adrenal neoplasms were identified incidentally by ultrasonography, and tumor in the left thyroid lobe was identified by palpation. Primary hyperparathyroidism was diagnosed by biochemical testing. Histopathology report was consistent with diagnosis of bilateral pheochromocytoma and parathyroid adenoma. Immunohistochemical staining was positive for calcitonin and synaptophysin, and negative for thyroglobulin, which confirmed medullary thyroid carcinoma. This case in a dog is presenting neoplastic characteristics similar to human MEN 2A and emphasizing the importance of using immunohistochemistry for confirmation.