Thyroid cancer in children is mainly of the differentiated type and the vast majority of them are mainly papillary and follicular carcinomas, which are not sensitive to radiotherapy and chemotherapy, and surgery is the main treatment. However, for many children with thyroid cancer, the end of surgery does not mean the end of treatment, and the subsequent endocrine therapy and possible iodine 131 treatment should be given sufficient attention. With 5 factors I131 therapy should be done after surgery Some parents ask in the clinic if I131 therapy should be done after surgery. It is true that a significant number of children with thyroid cancer need this adjuvant treatment after surgery. On the one hand, it is to remove potential or hidden local cancer foci and metastases. For locally advanced thyroid cancer with residual tumors or metastases, I131 isotope therapy can destroy the residual intraoperative lesions or metastases, especially for distant metastases, I131 isotope therapy plays a very important role. On the other hand, I131 treatment can remove residual thyroid tissue from the body so that the doctor can know whether there is recurrence and metastasis of thyroid cancer according to the HTg level in the blood. To some extent, I131 is equivalent to chemotherapy. However, I131 has fewer side effects and does not cause significant damage to major organs of the body, no bone marrow suppression, no significant gastrointestinal reactions, and generally no decrease in white blood cells or discomfort such as hair loss or vomiting. The main side effect of I131 treatment is damage to parotid tissue. A small number of patients have dry mouth after treatment. Some patients may also experience neck swelling and pain after initial I131 treatment. This is mainly due to the inflammatory response of the residual thyroid tissue during treatment, which mostly resolves with symptomatic treatment. Although some scholars believe that I131 treatment has the risk of secondary tumors, most studies have shown that postoperative I131 treatment for thyroid cancer in children has not resulted in secondary malignancies such as leukemia, so it is generally considered that reasonable I131 treatment is safe and effective. Generally, I131 therapy is required for ① tumor diameter R1.5cm, ② tumor diameter less than 1.5cm but multifocal, ③ tumor involving thyroid envelope or extra-glandular organs, ④ lymph node metastasis, and ⑤ distant metastasis. The dose and frequency of I131 treatment will depend on the patient’s specific condition and sensitivity to I131. In children with thyroid cancer with lymph node metastasis but no distant metastasis, I131 treatment should be administered about three times after surgery. Overall, thyroid cancer that is sensitive to I131 has better treatment results, but this method is not a substitute for surgery! Even for a tumor about 2cm in size, relying only on I131 treatment, at least 6 times more treatments are needed. Therefore, for thyroid cancer, you should try to remove it surgically if you can. Without I131 treatment, all patients should take thyroxine tablets for a long time. After thyroid cancer surgery, all patients should receive endocrine therapy, i.e. oral thyroxine tablets, except for some children who need to receive I131 treatment. The thyroid gland is vital to the body’s metabolism. After total removal, thyroxine tablets are required. This is for two reasons: first, thyroxine is needed for human metabolism and must be supplemented in vitro to meet the physiological needs of the body, especially for children, as a lack of thyroxine can have an incalculable negative impact on their growth and intellectual development; second, thyroxine tablets can inhibit the secretion of TSH and thus inhibit the recurrence and metastasis of thyroid cancer, which is known as endocrine therapy. The mechanism is that most differentiated thyroid cancers are TSH-dependent tumors and their growth is stimulated by TSH, so inhibiting TSH secretion can achieve the purpose of inhibiting the growth and metastasis of thyroid cancer. Too little will lead to hypothyroidism, which will adversely affect the growth and development of the child, while too much will lead to hyperthyroidism. When taking thyroxine tablets after thyroid cancer surgery, the dose is usually high and the TSH should be controlled to less than 0.1 mU/L. It would be better if it can be controlled to less than 0.01 mU/L, but care should be taken to prevent hyperthyroidism. Therefore, after thyroid cancer surgery, children should have their thyroid function checked regularly and the oral dose of thyroxine tablets should be adjusted according to TSH, T3 and T4 levels, usually at least once every six months. Post-operative review 3-6 months Post-operative review of thyroid cancer is necessary to detect any recurrence or metastasis in time. The examination items include blood test for thyroid function and HTg, ultrasound of the thyroid gland in the neck, ultrasound of the abdomen, chest X-ray, etc. Depending on the situation, CT and MRI of the neck can be performed, and if possible, PET-CT can be performed. When children are ready to receive I131 treatment after thyroid cancer surgery, they should stop eating seafood and other seafood for one month before treatment, stop taking thyroxine tablets and avoid eating iodized salt in their diet. When thyroxine tablets are first started, thyroid function should be retested in 1-2 months, and after thyroid function is adjusted to a satisfactory level, it can be retested once every six months. It is also necessary to avoid overexertion in daily life. The rate of recurrence is related to the standard of surgery and the malignancy of the tumor. If the tumor is highly malignant, the recurrence rate is high; if it is less malignant, the recurrence rate is also relatively low. Generally speaking, the recurrence rate of differentiated thyroid cancer is less than 10% after standardized treatment. Regular postoperative review helps to detect any tumor recurrence and metastasis in time. When HTg is significantly higher than normal, it indicates the possibility of local recurrence and metastasis; if a lump reappears in the neck surgery area, relevant examination should be performed to exclude the recurrence of local primary site and regional lymphatic drainage metastasis site. The treatment of recurrent tumor is much more complicated than the first recurrence and requires comprehensive consideration of the child’s physical condition, recurrence site and involved organs. To summarize: reasonable and standardized treatment is very important for the prognosis and prevention of recurrence of thyroid cancer in children. Thyroidectomy, cervical lymph node dissection, TSH suppression therapy and adjuvant I131 therapy can effectively prevent recurrence, improve patients’ survival quality and significantly improve prognosis.