Thyroid cancer is a malignancy that starts in the thyroid gland. To understand thyroid cancer, it helps to know about the normal structure and function of the thyroid gland. The thyroid gland is below the thyroid cartilage (Adamís apple) in the front part of the neck.
In most people, the thyroid cannot be seen or felt. It is butterfly shaped, with 2 lobes joined by a narrow bridge of tissue called the isthmus. The thyroid gland has 2 main types of cells: Follicular cells use iodine from the blood to make thyroid hormones, which help regulate a personís metabolism. C cells make calcitonin, a hormone that helps control how the body uses calcium.
Many types of growths and tumors can develop in the thyroid gland. Most of these are benign (non-cancerous) but others are malignant. Papillary carcinoma: About 8 out of 10 thyroid cancers are papillary carcinomas. Papillary carcinomas tend to grow very slowly and usually develop in only one lobe of the thyroid gland. Even though they grow slowly, papillary carcinomas often spread to the lymph nodes in the neck. Still, these cancers can usually be treated successfully and are rarely fatal.
Follicular carcinoma: This is the next most common type, making up about 1 out of 10 thyroid cancers. It is more common in countries where people donít get enough iodine in their diet. These cancers usually do not spread to lymph nodes, but they can spread to other parts of the body, such as the lungs or bones. The outlook (prognosis) for follicular carcinoma is not quite as good as that of papillary carcinoma, although it is still very good in most cases. These cancers are treated with surgery and often radioactive Iodine therapy.
Anaplastic carcinoma: Also called undifferentiated carcinoma is a rare form of thyroid cancer, making up about 2% of all thyroid cancers. It is highly aggressive and spreads early and extensively.
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. Because MTC 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, which accounts for about 8 out of 10 cases of MTC, is not inherited (meaning 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 cancers.