Abstract
Thyroid function tests are usually of little value in the evaluation of thyroid nodules, with the exception of possible toxic adenomas. Thyroglobulin levels may be elevated in patients with thyroid malignancy and are very useful as a tumor marker in the routine follow up of patients operated upon for thyroid cancer (1,2),but preoperative blood levels do not differentiate from those associated with benign adenomas or thyroiditis. Serum antithyroglobulin and antimicrosomal (or antithyroid peroxidase) antibodies are also of very limited value (1). Special diagnostic studies are available for the detection of medullary thyroid cancer (MTC), which may present as a dominant cold nodule per se or as part of a multiple endocrine neoplasia (MEN) syndrome (3,4). MEN 2A is characterized by MTC with pheochromocytoma and, in some cases, hyperparathyroidism. The familial MTC of MEN 2A differs from sporadic MTC in being often preceded by C cell hyperpasia leading to multifocal tumors. MEN 2B includes MTC, pheochromocytoma, and several phenotypic abnormalities including mucosal neuromata. It has been shown that the RET protooncogene is the gene responsible for MEN 2A and 2B, and mutations in differing codons and exons of RET have been identified in sporadic MTC as well. It is now possible to routinely identify RET in material obtained by fine needle aspiration of a thyroid nodule. Differentiation between the mutations known for sporadic vs familial MTC provides information that helps decide whether or not preoperative screening for pheochromocytoma is necessary. Traditional management approaches have held that basal plasma calcitonin or CEA (carcinoembryonic antigen), and calcium and/or pentagastrin stimulation tests or assessment for the RET protooncogene intended to identify cases of MTC are not cost effective in the initial or routine evaluation of the nodular thyroid. However, some recent studies have indicated otherwise, i.e., that calcitonin measurements may detect unsuspected medullary carcinoma (5,6).
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