Thyroid Cancer Treatment (Professional)
General Information About Thyroid Cancer
Incidence and Mortality
Carcinoma of the thyroid gland is an uncommon cancer but is the most common malignancy of the endocrine system. Differentiated tumors (papillary or follicular) are highly treatable and usually curable. Poorly differentiated tumors (medullary or anaplastic) are much less common, are aggressive, metastasize early, and have a much poorer prognosis. Thyroid cancer affects women more often than men and usually occurs in people between the ages of 25 and 65 years. The incidence of this malignancy has been increasing over the last decade. Thyroid cancer commonly presents as a cold nodule. The overall incidence of cancer in a cold nodule is 12% to 15%, but it is higher in people younger than 40 years and in people with calcifications present on preoperative ultrasonography.[3,4]
Patients with a history of radiation administered in infancy and childhood for benign conditions of the head and neck, such as enlarged thymus, acne, or tonsillar or adenoidal enlargement, have an increased risk of cancer as well as other abnormalities of the thyroid gland. In this group of patients, malignancies of the thyroid gland first appear beginning as early as 5 years following radiation and may appear 20 or more years later. Radiation exposure as a consequence of nuclear fallout has also been associated with a high risk of thyroid cancer, especially in children.[6,7,8] Other risk factors for the development of thyroid cancer include the following:
The prognosis for differentiated carcinoma is better for patients younger than 40 years without extracapsular extension or vascular invasion.[10,11,12,13,14] Age appears to be the single most important prognostic factor. The prognostic significance of lymph node status is controversial. One retrospective surgical series of 931 previously untreated patients with differentiated thyroid cancer found that female gender, multifocality, and regional node involvement are favorable prognostic factors. Adverse factors included age older than 45 years, follicular histology, primary tumor larger than 4 cm (T2–T3), extrathyroid extension (T4), and distant metastases.[15,16] Other studies, however, have shown that regional lymph node involvement had no effect [17,18] or even an adverse effect on survival.[13,14,19]
Diffuse, intense immunostaining for vascular endothelial growth factor in patients with papillary cancer has been associated with a high rate of local recurrence and distant metastases. An elevated serum thyroglobulin level correlates strongly with recurrent tumor when found in patients with differentiated thyroid cancer during postoperative evaluations.[21,22] Serum thyroglobulin levels are most sensitive when patients are hypothyroid and have elevated serum thyroid-stimulating hormone levels. Expression of the tumor suppressor gene p53 has also been associated with an adverse prognosis for patients with thyroid cancer.
Patients considered at low risk by the age, metastases, extent, and size (AMES) risk criteria include women younger than 50 years and men younger than 40 years without evidence of distant metastases. Also included in the low-risk group are older patients with primary tumors smaller than 5 cm and papillary cancer without evidence of gross extrathyroid invasion or follicular cancer without either major capsular invasion or blood vessel invasion. Using these criteria, a retrospective study of 1,019 patients showed that the 20-year survival rate is 98% for low-risk patients and 50% for high-risk patients. The 10-year overall relative survival rates for patients in the United States are 93% for papillary cancer, 85% for follicular cancer, 75% for medullary cancer, and 14% for undifferentiated/anaplastic cancer.
The thyroid gland may occasionally be the site of other primary tumors, including sarcomas, lymphomas, epidermoid carcinomas, and teratomas and may be the site of metastasis from other cancers, particularly of the lung, breast, and kidney.
Other PDQ summaries containing information related to thyroid cancer include the following:
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