Immunohistochemistry of ultimobranchial thyroid carcinomas in seven slaughtered cows and one bull

Eight thyroid gland epithelial tumors were found in 7 cows and 1 bull in a retrospective study of thyroid gland lesions in slaughtered cattle. All tumors were classified as ultimobranchial thyroid carcinomas based on morphology and immunohistochemistry. All tumors consisted of solid sheets and nests of polygonal to oval epithelial cells, with more sparsely dispersed colloid-filled follicles. Connective tissue separating nests of epithelial cells varied from delicate fibrovascular stroma to dense collagenous stroma. Fusiform epithelial cells with rare neural fibers and ganglion cells were present in 1 tumor. Cells within solid areas of these tumors were immunoreactive for calcitonin, calcitonin gene-related peptide, neuron-specific enolase, and synaptophysin. Colloid and follicle cells were immunoreactive for thyroglobulin. Few follicle cells also were reactive for calcitonin gene-related peptide. Neoplastic cells invaded the fibrous capsules in all 8 cattle. These tumors represented proliferation of a mixed population of undifferentiated cells, C cells, and thyroid follicular epithelial cells, presumably derived from the thyroid ultimobranchial bodies. These ultimobranchial carcinomas in slaughtered cattle are comparable to ultimobranchial tumors described in dairy bulls and the intermediate type of thyroid gland carcinomas (mixed thyroid medullary carcinomas) described in human beings.