The thyroid needs iodine to properly produce the thyroid hormones. By administering radioactive iodine to a patient, the thyroid tissue will absorb the altered iodine, which then destroys that thyroid tissue. Examples of benign tumors are adenomas, which secrete thyroid hormone.
Malignant tumors are more rare and are found in many stages of malignancy.
Thyroid adenomas grow from the cell layer that lines the inner surface of the thyroid gland. The adenoma itself secretes thyroid hormone. If the adenoma secretes enough thyroid hormone, it may cause hyperthyroidism. Thyroid adenomas may be treated if they cause hyperthyroidism. Cancer of the thyroid occurs more often in people who have undergone radiation to the head, neck, or chest.