c l i n i c a l f o l i o s : d i s c u s s i o n

Medullary Thryoid Carcinoma



Related narrative: Radical Neck Dissection for Medullary Carcinoma of the Thyroid

Thyroid cancers are the most common endocrine cancers. They are dominated by well-differentiated carcinomas, including papillary carcinoma, which makes up about 80% of thyroid cancers, and follicular carcinoma, which makes up about 10% of thyroid cancers. (See also thyroid cancer and Hurthle cell thyroid cancer discussions.) Poorly differentiated cancers, such as medullary and anaplastic carcinomas are much less common, each about 5% of thyroid malignancies. They are aggressive, metastasize early, and have a much poorer prognosis. The 10-year survival for medullary carcinoma overall is reported at 60-70%

Diagnosis and Staging
The patient usually presents with a palpable nodule, and diagnosis is based on fine-needle aspiration cytologic examination. This method has a false-negative rate of less than 5% and a false-positive rate of 1% to 5%. Also, the MTC tumor cells secrete the polypeptide hormone calcintonin, which serves as a highly sensitive and specific biomarker-useful for defining the presence of disease, either preoperatively or after thyroidectomy. The clinical staging system of the AJCC correlates survival to size of the primary tumor, presence or absence of lymph node metastases, and presence or absence of distance metastasis. Patients with the best prognosis are those who are diagnosed by provocative screening, before the appearance of palpable disease.

Stage I: Tumor <1 cm in size or clinically occult disease detected by provocative biochemical screening (10-year survival is >95%).
Stage II: Tumor >1 cm but <4 cm (10-year survival is 50-95%).
Stage III: Lymph node metastasis (Ten-year survival is 15-50%).
Stage IV: Distant metastasis (10-year survival is <15%).

Near-total and total thyroidectomy with routine central and bilateral functional neck dissection (see modified neck dissection) are recommended to treat MTC. Removal of all the tissues with medullary cancer helps in long-term survival, so meticulous nodal dissection is important. A significant surgical risk for MTC patients undergoing compartment-oriented lymphadenectomy is permanent hypoparathyroidism. External beam radiotherapy gives no survival benefit, nor does radioactive iodine. Chemotherapy is of little benefit beyond the palliative.

Genetic Risk Factors
About 25% of the time, MTC presents as a familial tumor; the related syndromes are multiple endocrine neoplasia (MEN) IIA, (which is the most common, comprising MTC, pheochromocytomas, and parathyroid adenomas), MEN IIB (comprising MTC, pheochromocytomas, characteristic phenotypic facies, ganglioneuromas, and marfanoid features), and familial non-MEN syndromes. Virtually all patients with MEN-IIA, IIB, and familial syndromes develop MTC; therefore, identifying the genetic mutation and performing a thyroidectomy at an early age are vital. The RET proto-oncogene affects the development of inherited forms of MTC and is important in the clinical management of patients and their families. All patients with medullary carcinoma of the thyroid (whether familial or sporadic) should be tested for RET mutations, and if they are positive, then family members should also be tested. Whereas modest elevation of calcitonin may lead to a false-positive diagnosis of medullary carcinoma, DNA testing for the RET mutation is the optimal approach in evaluating MEN 2A. Family members who are gene carriers should undergo prophylactic thyroidectomy at an early age.


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This page was last modified on 17-Jan-2001.