Thyroid cancer is a malignant tumor of the thyroid gland, which is characterized by easy metastasis and recurrence. The main clinical manifestation is the growth of thyroid mass in the neck, and sometimes the mass may cause breathing difficulty and hoarseness due to compression. Except for 15-20% of undifferentiated carcinoma and medullary carcinoma which have higher malignancy, more than 80% of nail cancer is differentiated nail cancer, including papillary carcinoma, follicular carcinoma and mixed papillary-follicular carcinoma, which have lower malignancy, slower development and relatively benign nature. As long as these patients are detected early and treated regularly, they can achieve good treatment effects and even rarely cause death. Therefore, timely formal treatment in qualified hospitals is the key to overcome the disease. At present, it is believed that the formal treatment of differentiated nail cancer consists of three parts, one of which is indispensable. 1.Surgery to remove the primary lesion and the metastatic lesion that may be removed. 2.Destroying the residual thyroid tissue and hidden metastatic lesions after surgery with radioactive 131 iodine. 3. Lifelong thyroid hormone replacement therapy to correct hypothyroidism and inhibit the recurrence and growth of tumor. The necessity of surgical treatment for thyroid cancer is easily accepted and understood by everyone. However, many patients with thyroid cancer think that everything is fine once they have undergone surgery, especially when they feel good about their physical condition, which is a very harmful concept. According to modern medical science, the second step, i.e. radioactive 131 iodine treatment, must be carried out after the surgery of nail cancer, and the surgery alone is not enough. Firstly, many metastases of nail cancer, especially distant and extensive metastases, such as lung and bone, are difficult to be removed by surgery. Secondly, in order to avoid damaging the parathyroid glands and the laryngeal nerve, it is impossible to remove all thyroid tissues during surgery, and there are always residual thyroid tissues. In contrast, thyroid cancer is often multifocal, which means that each cell group in the thyroid gland may hide cancer. According to foreign data, 62.5~87.0% of postoperative residual thyroid tissues can be seen as cancerous lesions under microscope, which are the root cause of recurrence and metastasis in the future. Thirdly, the residual thyroid tissues after surgery often make many proven methods of modern medicine to detect recurrence and metastasis of nail cancer much less sensitive, making it impossible to make early diagnosis and delaying treatment. Therefore, it is of great clinical significance to remove residual thyroid gland and destroy the metastases that cannot be removed surgically after nail cancer surgery. To achieve this purpose, modern medicine has developed the easiest and most effective method, which is oral radioactive iodine 131. After the residual thyroid tissue is removed after surgery, most of the metastases have the ability to take in radioactive 131 iodine. Therefore, after oral administration of radioactive 131 iodine, it can reach the lesion like a biological missile and use the b-rays it releases to destroy the lesion and achieve the treatment purpose. The treatment method of 131 iodine treatment for nail cancer is very simple, which requires only one oral dose and a few days of hospitalization for observation, and then the whole treatment is finished. According to overseas data, the recurrence rate of nail cancer is as high as 32.0% with surgery alone, 11.0% with surgery and oral thyroid hormone, and only 2.7% with surgery + 131 iodine therapy + oral thyroid hormone. According to foreign data, the mortality rate of patients with surgery alone is 3.8-5.2 times higher than that of those treated with surgery + 131 iodine, and the recurrence rate is 4 times higher than that of those treated with surgery + 131 iodine. 131 iodine has an efficiency of 75% in the treatment of metastatic foci of differentiated nail cancer. Therefore, 131 iodine therapy is an essential and important part of the treatment plan for differentiated nail cancer. All patients with differentiated nail cancer, such as papillary, follicular or mixed carcinoma, should be routinely treated with 131 iodine to remove residual thyroid tissue for long-term benefit, regardless of the presence or absence of conscious symptoms; 131 iodine should also be applied to destroy metastases if they have the ability to take up 131 iodine. 131 iodine treatment for thyroid cancer is a kind of biological missile treatment, in which the drug only reaches the diseased tissues and has less impact on other organs and tissues of the whole body, so it is a treatment method with less side effects and complications. From the perspective of immediate reactions, generally speaking, in the first few days after taking the drug, there may be loss of appetite, poor mental health, dizziness, neck swelling and pain, etc. Most of them are not very serious and will disappear on their own after a few days without special treatment. In terms of long-term reactions, most scholars have not found complications such as leukemia and permanent bone marrow suppression, nor does it affect fertility. Therefore, patients of any constitution can generally tolerate it. Of course, hypothyroidism is bound to occur after the treatment, which is the goal of the treatment, and it is not a negative consequence for patients with thyroid cancer. Low thyroid can be rapidly corrected with thyroid hormone replacement therapy. In addition, thyroid hormone can inhibit the recurrence and growth of nail cancer lesions, which is required even without 131 iodine treatment. Therefore, it is an essential step in the treatment plan. It is important to note that nail cancer is a general term for malignant tumors of the thyroid gland, which includes many categories and their treatment measures vary. Then again, the presence of a mass in the neck may not always be nail cancer. Therefore, first of all, a clear diagnosis should be made before proper treatment plan and correct treatment method can be selected. All patients with lumps in the neck should go to qualified hospitals for early diagnosis and treatment in a timely manner. 131 iodine treatment for nail cancer is an emerging advanced technology, which generally requires hospitals with advanced equipment and experience to carry out.