Medullary carcinoma of the thyroid gland.

Medullary thyroid carcinoma (MTC) is an uncommon thyroid tumor that has attracted a great deal of interest because of its frequent presentation as a familial tumor and its primary involvement in the type II multiple endocrine neoplasia (MEN) syndromes MEN-IIA and MEN-IIB and familial medullary thyroid carcinoma (FMTC). The MTC tumor cells secrete the polypeptide hormone calcitonin, which serves as an excellent tumor marker, useful for defining the presence of disease, preoperatively or following thyroidectomy. The discovery that mutations in the RET proto-oncogene are associated with MEN-II syndromes was highly significant in that it demonstrated a clear correlation between genotype and phenotype; and most importantly it provided a mechanism whereby family members at risk could be identified by direct DNA analysis. Virtually all patients with MEN-IIA, MEN-IIB, and FMTC develop MTC; therefore there is a clear rationale for performing thyroidectomy as soon as a RET mutation has been identified. Because MTC appears to be much more aggressive in patients with MEN-IIB, thyroidectomy is performed during the first year of life in this setting, whereas in patients with MEN-IIA, where the tumor appears to be more indolent, the procedure can be safety delayed until age 5 years. Reoperative neck exploration in patients with evidence of persistent or recurrent MTC has been effective in a significant number of patients, although the success of the operation requires careful patient selection and preoperative assessment. MTC, as expressed in the MEN-II syndromes, is an excellent model to evaluate the usefulness of interventional therapy in patients demonstrated to have a genetic predisposition for cancer.