Why is iodine-131 needed for “debulking” treatment of differentiated thyroid cancer? Since thyroid cancer (especially papillary cancer) has a tendency to grow multifocally, there may be residual thyroid cancer foci in the residual thyroid tissue. -131 can find the residual thyroid tissue and the residual thyroid cancer lesions in the body and destroy the residual thyroid tissue and the possible tumor lesions by releasing beta rays during the decay of iodine-131. Why can Iodine-131 also treat metastatic foci of differentiated thyroid cancer? The thyroid gland produces thyroid hormones, and iodine is one of the necessary substances for the synthesis of thyroid hormones. Iodine-131 has the same chemical properties as iodine and can be selectively taken up by the thyroid gland after oral administration. Most of the differentiated thyroid cancers such as papillary thyroid cancer and follicular carcinoma also retain the function of iodine uptake. Therefore, after the normal thyroid tissue is removed, these thyroid cancer cells can uptake iodine and use the radiation emitted by iodine-131 to effectively destroy the tumor cells in local and distant metastatic lesions to prevent and control tumor progression. What treatments are needed for differentiated thyroid cancer? Most well-differentiated thyroid cancers are treated in three steps: (1) total thyroidectomy; (2) iodine-131 therapy; and (3) thyroid hormone suppression therapy. Patients treated with iodine-131 have a significantly lower chance of recurrence and metastasis compared to those treated with surgery only.