Overview of Thyroid Cancer
From Statistics to Types
Thyroid Cancer: By the Numbers
Thyroid cancer is the most common malignancy of the endocrine system,1 and has shown a significant increase in incidence in both men and women since 1980. The National Cancer Institute’s (NCI) report, Surveillance Epidemiology and End Results (SEER) provides a wealth of data regarding thyroid cancer (Table 1).
Table 1: Statistical Overview of Thyroid Cancer2
|Median age for diagnosis, 2005-09||50|
|Median age for death, 2005-09||73|
|Estimated of number of people who will be diagnosed with thyroid cancer in 2012||Total: 56,460
|Estimated of number of deaths expected from thyroid cancer in 2012||Total: 1,780
|Prevalence of thyroid cancer, January 1, 2009||Total: 496,901
|Lifetime risk to be diagnosed with thyroid cancer for those born in 2009||1.03%|
Thyroid Nodules and Types of Thyroid Cancer
Thyroid nodules are a common finding in the clinical setting. These abnormal growths may be seen or felt at the base of the neck anteriorly. Palpable thyroid nodules are present in approximately 1% of men and 5% of women.3 Thyroid nodules may be detected incidental to imaging performed to diagnose an unrelated disorder.
Nodules can be solid, fluid filled (cystic), or mixed (solid and cystic). Purely cystic nodules appear to have a lower risk of cancer. While most thyroid nodules are benign, all thyroid nodules require careful and thorough examination as 5% to 15% can be malignant.3
Follicular and Parafollicular Cells (C Cells)
The thyroid gland is composed of follicular and parafollicular cells that secrete different hormones essential to regulating metabolism.
- Follicular cells secrete thyroxine (T4) and triiodothyronine (T3), which are iodine-containing hormones.
- Parafollicular cells or C cells secrete calcitonin, a hormone that plays a role in calcium homeostasis.
Certain types of thyroid cancers—those classified as differentiated thyroid cancers—originate from follicular cells, and account for about 90% of all thyroid cancers.4
Differentiated Thyroid Cancer (DTC) Types
- Papillary or papillary adenocarcinoma constitutes 70% to 80% of DTC cases. It is a slow-growing cancer that may invade lymph nodes. It rarely metastasizes outside the neck. Even when papillary thyroid cancer metastasizes to a lymph node(s), the prognosis is good.5
- Follicular or follicular adenocarcinoma occurs in approximately 10% of DTC cases. It usually does not metastasize to the lymph nodes, but may spread to the bones, lungs, or other organs. The prognosis is good.5
- Hürthle cell carcinoma is also called oxyphil cell carcinoma. It is a subtype of follicular thyroid cancer and constitutes about 3% of DTC. Hürthle cell thyroid cancer is difficult to confirm prior to surgery because cytology from fine-needle aspiration may be indeterminate. It is often difficult to treat because it does not concentrate radioactive iodine.
Other Thyroid Cancers
- Medullary thyroid cancer accounts for about 5% of thyroid carcinomas.6 It arises from the parafollicular cells. While most medullary thyroid cancers are sporatic, approximately 25% are familial.6 A family history of multiple endocrine neoplasia (MEN) type 2 and/or prior history of pheochromocytoma (adrenal gland tumor) or hyperparathyroidism should raise the suspicion of possible medullary thyroid cancer in a person with a thyroid nodule. The prognosis is not as favorable as that of differentiated thyroid carcinomas.
- Anaplastic thyroid cancers are rare (~2%) and aggressive. More than half the deaths attributable to thyroid carcinoma are due to anaplastic cancers. It usually presents as a rapidly growing neck mass with distant metastases. Most patients are elderly.6
- Thyroid lymphoma is rare. It may be observed in patients with a goiter that has rapidly developed in a short period of time. Symptoms may include dysphagia and hoarseness. Approximately 50% of primary thyroid lymphomas occur in pre-existing Hashimoto’s thyroiditis.6