Medullary thyroid carcinoma: recent advances and management update.

Medullary thyroid carcinoma (MTC) is a malignancy of the thyroid C-cells that comprises 5-10% of all thyroid cancers. MTC occurs in both sporadic and familial forms, the latter making up 25% of all MTCs and being comprised of three distinct syndromes--multiple endocrine neoplasia type 2A (MEN 2A), multiple endocrine neoplasia type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC). To date, screening for MTC has been performed using the pentagastrin stimulation test, which is a provocative test for calcitonin release. Germline mutations in the RET protooncogene have been identified in families manifesting these syndromes and genetic screening of individuals at risk of one of these syndromes has become integral to their clinical management. The majority of the mutations associated with MEN 2A and FMTC are tightly clustered in a cysteine-rich region of the RET receptor. A single mutation associated with MEN 2B is in the the tyrosine kinase domain of the RET receptor. Somatic mutations have been identified in the tumor tissue of individuals with sporadic MTC and may prove to be helpful markers in discerning the hereditary or sporadic nature of the MTC. There is general agreement that the primary operation for MTC should include total thyroidectomy and central neck lymph node clearance. The role of microdissection for recurrent disease awaits longitudinal evaluation. External radiotherapy, radionuclide therapy, and chemotherapy may have a role in palliation, but have not been proven to have a curative value. Prognostic factors are discussed.