1) This carcinoma comprises less than 10% of all thyroid cancers. This specific type as significant diagnostic importance because of its aggressive nature and its close association with multiple endocrine neoplasia syndromes. Approximately 10% to 20% of medullary thyroid carcinoma is familial. Patients usually present with a thyroid nodule that is painless and firm. In the majority of cases nodal metastases is present at diagnosis. Surgery is the preferred treatment for both primary therapy and recurrent cases. It is generally not very sensitive to radiation and almost unresponsive to chemotherapy. - 2002

2) Cancer that develops in C cells of the thyroid. The C cells make a hormone (calcitonin) that helps maintain a healthy level of calcium in the blood.