Calcitonin producing C-cell tumors (C-cell adenomas and carcinomas/ultimobranchial tumors) occur in a wide variety of domestic animals including bulls, horses, sheep, dogs and certain strains of laboratory rats. In general, the tumors develop in an age dependent manner with the highest frequency occurring in older animals. For example, up to 30% of aged bulls develop C-cell tumors (predominantly adenomas) and approximately 15 to 20% have C-cell hyperplasia. The tumors develop most commonly in bullsfed a high calcium diet while they occur rarely in cows. Affected bulls develop a series of skeletal abnormalities, including vertebral osteosclerosis with ankylosing spondylosis deformans, osteophytes, vertebral fractures and degenerative osteoarthrosis. Typically, blood calcium levels are in the normal-low normal range. Both lymph node and pulmonary metastases may occur. Pheochromocytomas may develop in association with C-cell tumors, and in some bovine breeds (Guernsey), an autosomal dominant mode ofinheritance has been proposed. In contrast to their high frequency in bulls, C-cell carcinomas (medullary thyroid carcinomas/MTC) account for less than 10% of human thyroid malignancies.
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