Medullary thyroid carcinoma (MTC) accounts for 5-10% of all thyroid cancers. The majority are sporadic cases occurring in elderly people. About one-quarter of the cases are familial with an autosomal dominant expression and present as one of three distinct clinical syndromes: multiple endocrine neoplasia (MEN) 2A, MEN 2B and familial medullary thyroid cancer (FMTC). MEN 2A is associated with pheochromocytomas and hyperparathyroidism. The 2B form is associated with pheochromocytomas and mucosal and gastrointestinal neuromas, while non-MEN FMTC has none of these associations.
The diagnostic hallmark of MTC is an elevation of the serum calcitonin level. The low incidence of the disease, relative to the incidence of nodules, makes it impractical to perform the assay on every patient presenting with a thyroid mass. The assay ought to be performed when malignancy is suspected and FNA has not indicated a follicular-derived lesion.
Mutations of the Ret proto-oncogene, a single trans-membrane growth factorlike receptor, result in the familial disorders multiple endocrine neoplasia Types 2A and 2B and FMTC: each of these conditions features the development of MTC. Genetic screening of potentially affected patients for the presence of these germ line mutations is now readily available and has proven more effective than screening via serial challenges with pentagastrin/calcium to detect abnormal calcitonin responses. Testing with pentagastrin/calcium was often performed in follow up of patients previously treated for medullary carcinoma but pentagastrin is no longer being commercially produced.
For patients with the familial forms of medullary carcinoma, the preoperative workup must address not only the thyroid mass but also the possibility of associated endocrinopathies. If pheochromocytomas are suspected, 24-hour urinary metanephrines should be measured. CT or MRI may be used to determine whether there are adrenal mass lesions but neither modality is able to determine the functional
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