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Thyroid Cancer



Related narrative: Follicular Thyroid Cancer


Thyroid cancers are the most common endocrine cancers, and the incidence has been increasing over the last decade. Thyroid cancer affects women more commonly than men, and the majority of cases occur in patients between the ages of 25 and 65. Patients with a history of radiation administered in childhood for benign conditions of the head and neck have an increased risk of thyroid cancer, and inherited gene mutations are associated with certain medullary and papillary tumors.

Thyroid tumors 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. Hurthle cell tumors are classified as a type of follicular carcinoma, representing about a quarter of the diagnoses in that category. Papillary carcinoma has an 80-90% 10-year survival, and follicular tumors are associated with a 65-75% 10-year survival rate.

Poorly differentiated cancers, such as medullary and anaplastic carcinomas are much less common, each representing about 5% of thyroid malignancies. About 25% of medullary thyroid cancers are genetically based; the RET proto-oncogene affects their development and is important in the clinical management of affected patients and their families. The 10-year survival for medullary carcinoma overall is reported at 60-70%. (See also medullary thyroid carcinoma and Hurthle cell thyroid cancer discussions.) Anaplastic tumors are aggressive with virtually no chance of long-term survival for the patient.

Rare and unusual forms of thyroid cancer include the tall cell variant (TCV) form of papillary carcinoma, insular thyroid cancer, squamous cell carcinoma, and thyroid lymphoma.

• TCV is associated with larger-sized tumors in older patients. Soft-tissue involvement, tumor recurrence, and metastasis are more prevalent features of TCV compared with typical papillary carcinoma.

• Insular thyroid cancer comprises solid clusters of tumor cells with small follicles that resemble pancreatic islet cells. Insular thyroid cancer may also be seen variably in typical papillary or follicular thyroid tumors. Though this type of cancer is aggressive on its own, when seen within well-differentiated tumors, it does not usually affect the prognosis. When a tumor has a majority insular component, there is a higher rate of recurrence, and probably a higher mortality rate.

• Squamous cell carcinoma represents approximately 1% of all thyroid cancers, and often occurs in elderly men with history of thyroid gland enlargement (e.g., goiter). It usually progresses rapidly, and complete surgical resection after early detection is the best chance for a cure.

• Primary thyroid lymphoma is frequently associated with Hashimoto's thyroiditis. Treatment is somewhat controversial, but an aggressive protocol includes thyroidectomy, plus radio- and chemotherapy. Survival rates have been reported from 30 to 80%.

Diagnosis and Staging

The patient generally 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%. Fine-needle aspiration does not effectively diagnose follicular-cell cancers because they require histologic demonstration of capsular or vascular invasion. The AJCC bases its tumor classification by the cellular type of tumor, size of tumor, lymph node and distant metastasis, and age of patient. A full description of the staging of thyroid carcinomas can be found at http://www.cancernet.nci.nih.gov

In general, patients can be classified as low- and high-risk based on their age, metastases, extent, and size of the tumor. Data showed a 20-year survival for low-risk patients to be 98% and 50% for high-risk patients. The incidence of regional nodal metastasis in thyroid cancer varies between 20-70%, depending on whether the tumor is papillary or follicular. Metastasis to local lymph nodes does not worsen the prognosis of either of those carcinomas. It is generally highest in papillary cancer – the most common form. However, long-term survival is good and recurrence is usually no greater than 10-20%. Papillary tumors metastasize usually through the lymph system, while follicular tumors travel through blood vessels. The presence of vascular invasion is a poor prognostic factor in follicular tumors, and the prognosis for patients with distant metastasis – usually to the lungs or bone – is poor.


• Differentiated Tumors: Papillary and Follicular
Differentiated thyroid cancers are treated primarily by surgery – sometimes with a lobectomy (including excision of the lobe and isthmus), but more often with a near-total or total thyroidectomy. The first procedure is associated with a lower complication rate, but the risk of recurrence is higher. I-131 radioiodine ablation therapy, which is effective against nodal recurrence, is compromised by the presence of the remaining lobe. Total thyroidectomy allows the patient to become hypothyroid in preparation for radiotherapy ablation. I-131 therapy is in addition to exogenous thyroid hormone treatment, which suppresses thyroid-stimulating hormone. Both have been shown to effectively decrease the recurrence of papillary and follicular tumors. External-beam radiation can be used for patients whose lesions are unresponsive to I-131. Standard treatment would also include the removal of any involved lymph nodes. At this time, the use of chemotherapy with any type of thyroid cancer is palliative at best; however, there have been some positive results, and clinical trials are ongoing. For patients undergoing total thyroidectomy, about 1% are at risk for permanent recurrent laryngeal palsy, and 2-5% at risk for permanent hypoparathyroidism. In the hands of an experienced surgeon, the overall complication rate has been reported to be about 3%.

• Poorly Differentiated Tumors: Medullary and Anaplastic

Near-total and total thyroidectomy with routine central and bilateral functional neck dissection (see modified neck dissection) are recommended to treat medullary thyroid cancer. Removal of all the tissues with medullary cancer helps in long-term survival, so meticulous nodal dissection is important. A significant surgical risk for 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. For anaplastic tumors, treatment is palliative by surgical debulking, and tracheostomy is frequently necessary. Some patients may benefit from local radiotherapy or occasionally chemotherapy; doxorubicin and cisplatin achieve partial remission in approximately 30% of patients. However, long-term prognosis with this tumor is dismal.


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This page was last modified on 14-Feb-2001.