Background: Medullary thyroid carcinoma (MTC) is sporadic in the great majority of cases but is the sine qua non of multiple endocrine neoplasia type 2 (MEN 2), an autosomal dominantly inherited cancer syndrome. Depending on the tissues affected, MEN 2 is divided into 3 subtypes. MEN 2A is characterized by the presence of MTC, pheochromocytoma and hyperparathyroidism. MEN 2B is characterized by MTC, pheochromocytoma and typical stigmata. FMTC comprises MTC as the only disease feature. Germline mutations in theRET protooncogene, which encodes a receptor tyrosine kinase, have been shown to cause all 3 subtypes of MEN 2.