Radioactive iodine therapy helps people live longer if they have papillary or follicular thyroid cancer (differentiated thyroid cancer) that has spread to the neck or other body parts, and it is now standard practice in such cases. But the benefits of RAI therapy are less clear for people with small cancers of the thyroid gland that do not seem to have spread, which can often be removed completely with surgery. Radioactive iodine therapy cannot be used to treat anaplastic (undifferentiated) and medullary thyroid carcinomas because these types of cancer do not take up iodine.
