The thyroid gland is located at the bottom of the neck. It makes hormones that help control the body's rate of metabolism (regular chemical processes of the body). Sometimes, the thyroid gland develops abnormal growths, often called nodules. The growths are usually small, and they can be solid or cystic (filled with fluid). Most nodules are benign, but some are cancerous. Doctors use blood tests, special scans, and needle aspiration to determine which growths are benign or cancerous. Benign nodules are followed closely because doctors typically regard nodules that increase in size as suspicious for malignancy. They often repeat needle aspiration of the nodules that increase in size to check for malignancy. However, whether change in size reliably identifies nodules that are cancerous has not been well studied.