Thyroid cancer is a disease in which malignant (cancer) cells form in the tissues of the thyroid gland. The thyroid is a gland at the base of the throat near the trachea (windpipe). It is shaped like a butterfly, with a right lobe and a left lobe. The isthmus, a thin piece of tissue, connects the two lobes. A healthy thyroid is a little larger than a quarter. It usually cannot be felt through the skin.
The thyroid uses iodine, a mineral found in some foods and in iodized salt, to help make several hormones. Thyroid hormones do the following:
- Control heart rate, body temperature, and how quickly food is changed into energy (metabolism).
- Control the amount of calcium in the blood.
There are different types of thyroid cancer, and they can be described as either:
- Differentiated thyroid cancer, which includes well-differentiated tumors, poorly differentiated tumors, and undifferentiated tumors; or
- Medullary thyroid cancer
There are four main types of thyroid cancer:
1. Papillary thyroid cancer
This is the most common type of thyroid cancer. In the United States, papillary thyroid cancer makes up about 80% of all thyroid cancer cases. It begins in follicular cells and grows slowly. If diagnosed early, most people with papillary thyroid cancer can be cured.
2. Follicular thyroid cancer
Follicular thyroid cancer makes up about 15% of all thyroid cancers. It begins in follicular cells and grows slowly. If diagnosed early, most people with follicular thyroid cancer can be treated successfully.
3. Medullary thyroid cancer
Medullary thyroid cancer makes up about 3% of all thyroid cancers. It begins in the C cells, also called parafollicular cells, of the thyroid. Cancer that starts in the C cells can make abnormally high levels of calcitonin. Medullary thyroid cancer tends to grow slowly. It can be easier to control if it's found and treated before it spreads to other parts of the body.
4. Anaplastic thyroid cancer
Anaplastic thyroid cancer makes up about 2% of all thyroid cancers. It begins in the follicular cells of the thyroid. The cancer cells tend to grow and spread very quickly. Anaplastic thyroid cancer is very hard to control.