What is Thyroid Cancer?
Thyroid cancer is a type of cancer that develops in the thyroid gland. The thyroid gland is a butterfly-shaped gland in the front of the neck, just below the Adam’s apple, that wraps around the front of the windpipe. The thyroid gland has two lobes, one on each side of the windpipe, that are connected by a small piece of tissue in the middle (the isthmus). The thyroid gland is a part of the endocrine system, which is made up of glands that produce and control the hormones in the body. The thyroid gland produces hormones that regulate heart rate, blood pressure, body temperature, and energy metabolism.
Types of Thyroid Cancer
There are four main types of thyroid cancer, classified based on the types of cells where the cancer begins:
Papillary thyroid cancer is the most common type of thyroid cancer, accounting for about 80% of all cases. Papillary thyroid cancer is derived from thyroid follicular cells and it is usually slow-growing but may still spread to lymph nodes in the neck. However, Papillary thyroid cancer can occur in only one lobe of the thyroid and can be treated successfully by surgery only. In other cases, it can be found in both thyroid lobes. Papillary thyroid cancer has multiple variants (conventional-variant, follicular-variant, tall-cell variant, and columnar cell variant).
About 10-15% of all cases of thyroid cancer can be classified as follicular. Like papillary thyroid cancer, follicular thyroid cancer is derived from thyroid follicular cells and may also spread into the lymph nodes in the neck. However, it is slightly more aggressive and often also invades blood vessels and more frequently spreads to distant organs, such as the bones or lungs compared to papillary thyroid cancer. Hurthle cell carcinoma is a variant of follicular thyroid cancer.
Medullary thyroid cancer accounts for about 2% to 5% of all cases. Medullary thyroid cancer is derived from thyroid C-cells. It is hereditary in some cases and is caused by an inherited genetic mutation. Any person who has a family member with medullary thyroid cancer should be tested for the genetic mutation known to cause the disease, unless the patient with the cancer has already been found not to carry the mutation. This type of thyroid cancer can be more aggressive unless diagnosed early, and often spreads to the lymph nodes, lungs, or liver. There are two main types of medullary thyroid cancer: sporadic and familial.
- Sporadic MTC: This is the most common form of medullary thyroid cancer, and accounts for about 75% of all medullary diagnoses. It occurs mostly in older adults.
- Familial MTC: This is the hereditary form of medullary thyroid cancer. It commonly develops during childhood or early adulthood, but certain patients may show signs of development later in life.
Anaplastic thyroid cancer is the most aggressive form of the disease and accounts for only about 1% of all cases. Anaplastic thyroid cancer often spreads quickly into structures in the neck, such as the trachea, as well as other parts of the body. It is very aggressive and does not often respond well to treatment.
There are about 65,000 new cases of thyroid cancer in the United States each year, 75% of which are in women. This disease is relatively rare and accounts for only about 1% of all new cancer diagnoses; however, it is the fastest growing form of cancer in women in the U.S. Fortunately, thyroid cancer is usually slow-growing and can often be treated successfully.