The thyroid is a gland in the front of the neck. It produces hormones which control growth and development.
We don’t know exactly what causes thyroid cancer, but there are some risk factors. For example: inheriting a faulty gene from your parents (though this is rare); having previous radiotherapy (as a small child) and some rare genetic conditions. In most people the first sign of thyroid cancer is a lump or swelling in the neck that gradually gets bigger.
It is normally diagnosed with a biopsy, and treated with surgery, radioactive iodine, and hormone therapy.