A neuroendocrine carcinoma arising from the C-cells of the thyroid gland. It is closely associated with multiple endocrine neoplasia syndromes. Approximately 10% to 20% of medullary thyroid carcinomas are familial. Patients usually present with a thyroid nodule that is painless and firm. In the majority of cases nodal involvement is present at diagnosis. Surgery is the preferred treatment for both primary lesions and recurrences. This carcinoma is generally not very sensitive to radiation and almost unresponsive to chemotherapy.