Thyroid C-cell carcinoma with amyloid in a red fox (Vulpes vulpes schrenchki)

An amyloid-producing medullary thyroid carcinoma (MTC) in a red fox (Vulpes vulpes schrenchki) bred in a zoo was examined using histopathologic and im munohistochemical techniques. The neoplastic cells had an ill-defined cytop lasmic membrane and abundant, finely granular eosinophilic cytoplasm, conta ining numerous argyrophilic granules. The neoplastic tissues were divided i nto various sizes by a vascular connective stroma, which was partly fibrova scular with broad areas of hyalinization containing varied amounts of amylo id. Immunohistochemically, neoplastic cells showed reactivity to anti-calci tonin, neuron-specific enolase, somatostatin, and keratin antibodies. Howev er, amyloid in the stroma did not show immunoreactivity to the antibodies u sed. Histologic and immunohistochemical features of MTC in the present anim al were analogous to those of the C-cell carcinoma derived from thyroid C c ells (parafollicular cells) reported in humans and dogs.