Thyroid cancer is cancer that develops from the tissues of the thyroid gland. It is a disease in which cells grow abnormally and have the potential to spread to other parts of the body. Symptoms can include swelling or a lump in the neck. Cancer can also occur in the thyroid after spread from other locations, in which case it is not classified as thyroid cancer.Risk factors include radiation exposure at a young age, having an enlarged thyroid, and family history. There are four main types – papillary thyroid cancer, follicular thyroid cancer, medullary thyroid cancer, and anaplastic thyroid cancer. Diagnosis is often based on ultrasound and fine needle aspiration. Screening people without symptoms and at normal risk for the disease is not recommended as of 2017.Treatment options may include surgery, radiation therapy including radioactive iodine, chemotherapy, thyroid hormone, targeted therapy, and watchful waiting. Surgery may involve removing part or all of the thyroid. Five year survival rates are 98% in the United States.Globally as of 2015 3.2 million people have thyroid cancer. In 2012, 298,000 new cases occurred. It most commonly occurs between the ages of 35 and 65. Women are affected more often than men. Those of Asian descent are more commonly affected. Rates have increased in the last few decades which is believed to be due to better detection. In 2015 it resulted in 31,900 deaths.