ESSENTIALS OF DIAGNOSIS
Painless swelling in region of thyroid.
Thyroid function tests usually normal.
Possible history of childhood irradiation to head and neck region.
Positive thyroid FNA cytology.
The incidence of differentiated (papillary and follicular) thyroid carcinomas increases with age (Table 26–6). The overall female:male ratio is 3:1. The yearly incidence of thyroid cancer has been increasing in the United States, with the number of cases diagnosed annually reaching 52,000, probably as a result of the wider use of ultrasound, CT, MRI, and PET that incidentally find small thyroid malignancies. Thyroid cancer mortality has been stable, accounting for about 2000 deaths in the United States annually. Clearly, the increasing incidence of thyroid cancer has been mainly due to incidentally found tumors; however, some true increase in cancer incidence is possible. In routine autopsy series, thyroid papillary microcarcinoma (10 mm diameter or smaller) is found with the surprising frequency of 11.5%. Most thyroid cancers remain microscopic and indolent. However, larger thyroid cancers (palpable or greater than or equal to 1 cm in diameter) are more malignant and require treatment.
Table 26–6.Some characteristics of thyroid cancer. ||Download (.pdf) Table 26–6. Some characteristics of thyroid cancer.
| ||Papillary ||Follicular ||Medullary ||Anaplastic |
|Incidence ||Most common ||Common ||Uncommon ||Uncommon |
|Average age ||42 ||50 ||50 ||57 |
|Females ||70% ||72% ||56% ||56% |
|Invasion || || || || |
| Juxtanodal ||+++++ ||+ ||++++++ ||+++ |
| Blood vessels ||+ ||+++ ||+++ ||+++++ |
| Distant sites ||+ ||+++ ||++ ||++++ |
|123I uptake ||+ ||++++ ||0 ||0 |
|10-year disease-specific survival ||97% ||92% ||78% ||7.3% |
Pure papillary (and mixed papillary-follicular) carcinoma comprises about 80% of all thyroid cancers. It usually presents as a single thyroid nodule, but it can arise out of a multinodular goiter. Papillary thyroid carcinoma is commonly multifocal within the gland, with other foci usually arising de novo rather than representing intraglandular metastases. The tumor involves both lobes in 30% of patients.
Papillary thyroid carcinoma is generally the least aggressive thyroid malignancy. It tends to grow slowly and often remains confined to the thyroid and regional lymph nodes for years. In about 80% of patients, there are microscopic metastases to cervical lymph nodes. However, the malignancy may become more aggressive, especially in patients over age 45 years, and most particularly in older adults. The cancer may invade the trachea and local muscles and may spread to the lungs. Papillary thyroid carcinoma is caused by genetic mutations or translocations. Activating mutations of the Ras oncogene can cause benign thyroid adenomas or nodular goiter. Additional activating mutations in BRAF or TRK genes can lead to papillary carcinoma. About 45% of papillary thyroid carcinomas are caused by over expression of the ret protooncogene (RET) by the translocation of certain gene promoters to it, producing retPTC-1, retPTC-2, or retPTC-3. Radiation treatments to the head and neck region tend to cause ...