Awareness: September Is Thyroid Cancer Awareness Month
What is Thyroid Cancer?
Thyroid cancer is a cancer that starts in the thyroid gland. The thyroid gland is below the thyroid cartilage (Adam's apple) in the front part of the neck.
The 2 most common types of thyroid cancer are papillary carcinoma and follicular carcinoma. Hürthle cell carcinoma is a subtype of follicular carcinoma. All these types are differentiated tumors.
Other types of thyroid cancer, such as medullary thyroid carcinoma, anaplastic carcinoma, and thyroid lymphoma, occur less often.
Differentiated thyroid cancers
Differentiated thyroid cancers develop from thyroid follicular cells. In these cancers, the cells look a lot like normal thyroid tissue when looked at under a microscope.
Papillary carcinoma: About 8 of 10 thyroid cancers are papillary carcinomas (also called papillary cancers or papillary adenocarcinomas). Papillary carcinomas typically grow very slowly. Usually they develop in only one lobe of the thyroid gland, but sometimes they occur in both lobes. Even though they grow slowly, papillary carcinomas often spread to the lymph nodes in the neck. But most of the time, these cancers can be successfully treated and are rarely fatal.
Several different types of papillary carcinoma can be recognized under the microscope. Of these, the follicular type (also called mixed papillary-follicular variant) occurs most often. The usual form of papillary carcinoma and the follicular type have the same outlook for survival (prognosis), and are treated the same. Other types of papillary carcinoma (columnar, tall cell, diffuse sclerosis) are not as common and tend to grow and spread more quickly.
Follicular carcinoma: Follicular carcinoma is the next most common type of thyroid cancer. It is also sometimes called follicular cancer or follicular adenocarcinoma. Follicular cancer is much less common than papillary thyroid cancer, making up about 1 out of 10 thyroid cancers. It is more common in countries where people don't get enough iodine in their diet. These cancers usually remain in the thyroid gland. Unlike papillary carcinoma, follicular carcinomas usually don't spread to lymph nodes, but some can spread to other parts of the body, such as the lungs or bones. The prognosis for follicular carcinoma is probably not quite as good as that of papillary carcinoma, although it is still very good in most cases.
Hürthle cell carcinoma, also known as oxyphil cell carcinoma, is actually a kind of follicular carcinoma. It accounts for about 3% of thyroid cancers. The prognosis may not be as good as that of typical follicular carcinoma because this type is harder to find and treat. This is because it is less likely to absorb radioactive iodine, which is used both for treatment and to look for the spread of differentiated thyroid cancer.
Other types of thyroid cancers
Medullary thyroid carcinoma: Medullary thyroid carcinoma (MTC) accounts for about 4% of thyroid cancers. It develops from the C cells of the thyroid gland. Sometimes this cancer can spread to lymph nodes, the lungs, or liver even before a thyroid nodule is discovered. These cancers usually release calcitonin and carcinoembryonic antigen (CEA) into the blood, causing high levels of these when checked by blood tests. Calcitonin is a hormone that helps control the amount of calcium in blood. CEA is a protein made by certain cancers. Because medullary cancer does not absorb or take up radioactive iodine (used for treatment and to find metastases of differentiated thyroid cancer), the prognosis (outlook) is not quite as good as that for differentiated thyroid cancers. There are 2 types of MTC:
- Sporadic MTC, occurring in about 8 of 10 cases, is not inherited; that is, it does not run in families. It occurs mostly in older adults and affects only one thyroid lobe.
- Familial MTC is inherited and can occur in each generation of a family. These cancers often develop during childhood or early adulthood and can spread early. Patients usually have cancer in several areas of both lobes. Familial MTC is often linked with an increased risk of other types of tumors. This is described in more detail in the section "What are the risk factors for thyroid cancer?"
Anaplastic carcinoma: Anaplastic carcinoma (also called undifferentiated carcinoma) is a rare form of thyroid cancer, making up about 2% of all thyroid cancers. It is thought to sometimes develop from an existing papillary or follicular cancer. This cancer is called undifferentiated because the cancer cells do not look very much like normal thyroid cells under the microscope. This is an aggressive cancer that rapidly invades the neck, often spreads to other parts of the body, and is very hard to treat.
Thyroid lymphoma: Lymphoma is very uncommon in the thyroid gland. Lymphomas are cancers that develop from lymphocytes, the main cell type of the immune system. Most lymphocytes are found in lymph nodes, which are pea-sized collections of immune cells scattered throughout the body (including the thyroid gland). Lymphomas are discussed in the separate American Cancer Society document, Non-Hodgkin Lymphoma.
Thyroid sarcoma: These rare cancers start in the supporting cells of the thyroid. They are often aggressive and hard to treat. Sarcomas are discussed in the separate American Cancer Society document, Sarcoma: Adult Soft Tissue Cancer.
For more detailed information about the symptoms and treatment of Thyroid Cancer, please visit the American Cancer Society.