What is a defining characteristic of medullary carcinoma of the thyroid?

Medullary carcinoma of the thyroid is distinctly characterized by the production of calcitonin, which is a hormone involved in calcium metabolism, and its association with multiple endocrine neoplasia syndromes, particularly MEN II. The tumor arises from parafollicular C cells of the thyroid, which are responsible for producing calcitonin. The elevated levels of this hormone are often used as a tumor marker in diagnosing and monitoring the disease.

Additionally, medullary carcinoma is commonly associated with multiple endocrine neoplasia type II (MEN II), especially MEN IIA, which predisposes individuals to various tumors, including medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism. The genetic basis for these associations involves mutations in the RET proto-oncogene.

In summary, the defining characteristics of medullary carcinoma include both the production of calcitonin and its association with MEN syndromes, making the combination of these elements crucial for understanding the condition.