Thyroid cancer is a disease in which the thyroid cells become abnormal, grow uncontrollably, and form tumors. The thyroid is a butterfly-shaped gland, located at the base of the throat. It has two lobes, the left and the right. The thyroid gland makes hormones that regulate heart rate, blood pressure, body temperature, and metabolism. The hormones produced by the thyroid also affect the nervous system, muscles, and other organs, and play an important role in regulating childhood growth and development. The thyroid uses iodine, a mineral found in some foods, to make several of its hormones.

Thyroid cancers are grouped into four types, depending on how the cells look under the microscope. The four types are papillary, follicular, medullary, and anaplastic thyroid cancers. The cancers grow at different rates, so the aggressiveness of each cancer is different. Papillary and follicular cancer develops in the cells that...