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
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.
Ashok RS. Management of the neck in thyroid cancer. Otolaryngologic Clinics of North America, 31(5); 1998: 823-831.
Bi J, Lu B. Advances in the diagnosis and management of thyroid neoplasms. Curr Opin Oncol, 12(1); 2000: 54-59.
Chen H, Udelsman R Papillary thyroid carcinoma: justification for total thyroidectomy and management of lymph node metastases. Surg Oncol Clin N Am, 7(4); 1998: 645-663.
Dillman WH. The Thyroid-Part II. In: Goldman L, Bennett JC. (eds.) Cecil textbook of medicine. 21st ed. Philadelphia: W.B. Saunders; 2000: 1241-1250.
Giuffrida D, Gharib H. Current diagnosis and management of medullary thyroid carcinoma. Ann Oncol, 9(7); 1998: 695-701.
Mazzaferri EL. An overview of the management of papillary and follicular thyroid carcinoma. Thyroid, 9(5); 1999: 421-427.
McHenry CR, Sandoval BA. Management of follicular and Hurthle cell neoplasms of the thyroid gland. Surg Oncol Clin N Am, 7(4); 1998: 893-910.
Miller FR, Netterville JL. Surgical management of thyroid and parathyroid disorders. Med Clin N Am, 83(1); 1999: 247-259.
National Cancer Institute CancerNet. Thyroid Cancer (PDQ) Treatment for Health Professionals. Available from http://cancernet.nci.nih.gov/.
Udelsman R, Chen H. The current management of thyroid cancer. Adv Surg, 33(1); 1999:1-27.