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What Is Medullary Thyroid Cancer?

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  • Written By: Jo Dunaway
  • Edited By: S. Pike
  • Last Modified Date: 17 September 2016
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Approximately 35,000 Americans receive diagnoses of thyroid carcinomas annually, and on average, medullary thyroid cancer is around 3 percent of these. Unlike most thyroid cancers, medullary thyroid carcinomas start in the parafollicular cells, and a prime indicator is an overproduction of a hormone called calcitonin. Diagnoses are usually performed using ultrasonography guided fine-needle aspiration, and the nearby lymph nodes are also biopsied for metastases. There are four forms of medullary thyroid cancer; most of these forms require thyroidectomies as well as chemotherapies and external radiation, as medullary has a worse prognosis than other thyroid cancers and recurrence is more likely. Symptomology may not occur initially; in the case of Multiple Endocrine Neoplasia syndromes (MEN), often no symptoms appear, yet patients are diagnosed because of incidence in a family member, as this form is a genetically carried susceptibility.

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When symptoms do occur, they are typically due to the excessive calcitonin and gene products of calcitonin, which present themselves as diarrhea and skin flushing, often pointing to liver metastases. Physical examination may reveal a lump or nodule at the base of the neck. There may also be problems with breathing, jaundice, and abdominal pain, and trouble with swallowing or voice changes due to the growth of the nodules into nearby structures. Bone tenderness can also point to metastases in the bone; other organs that are metastatic candidates are lungs, brain, lymph nodes, and adrenal glands. Immediate thyroidectomy is the initial treatment recommended for these symptoms in all forms of medullary thyroid cancer excepting the MEN syndromes.

The MEN syndromes are highly familial and make up around 25 percent of incidences of medullary thyroid cancer, such as the mutated gene determinant MEN-II-A, which is genetically distinct from MEN-II-B and may have hyperparathyroidism and pheochomocytoma accompanying the medullary cancer. If pheochomocytoma is present, it must be treated prior to a thyroidectomy. MEN-II-B will have only the pheochomocytoma endocrine disease as well as medullary thyroid cancer. Another form of medullary carcinoma is known as Sporadic medullary thyroid cancer; around 60 percent of medullary cancers are of this type and in nearly all cases do not metastasize at all. The remaining form of medullary thyroid cancer is also an inherited carcinoma type due to gene mutation, but it is the least aggressive of all the medullary forms, though it sometimes metastasizes through the blood and lymph systems to other organs.

After the thyroidectomy, which involves removal of the thyroid gland as well as nearby lymph nodes, the follow-up care consists mainly of some chemotherapies as well as regular tests for recurrence. Use of radioactive iodine is not indicated as, unlike other thyroid carcinomas, medullary thyroid cancer cells are not of a cell type that can absorb or react to radioactive iodine. External radiation beam therapy is usually used to prevent recurrences and to provide palliative care for those who are ineligible for surgery. Yearly chest X-rays and biennial tests of the blood to check for excessive calcitonin are usually indicated.

Prognoses are related to the stage of the cancer when discovered and treated. For stage one, the five-year survival rate is at 100 percent, for stage two, it is 98 percent, for stage three, it drops to 81 percent and at stage four, the five-year survival rate is 28 percent. The overall percentage for 10-year survival is 65 percent. Prognostic factors that might affect these numbers are advanced age, prior neck surgeries, and the MEN-II-B neoplasia syndrome, all of which correlate with poorer outcomes. From morbidity statistics internationally, the medullary thyroid cancer rates are very similar to those in the United States.

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