Medullary carcinoma of thyroid gland

**Definition:** 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.