Early textbooks advocated mass excision + lymph node dissection for thyroid cancer patients, while preserving about 20% of normal thyroid tissue, with the aim of maintaining the body’s physiological need for thyroid hormones. So why do you advocate total excision as much as possible today? There are the following factors: 1. Although thyroid cancer is clinically manifested as a single nodule in the thyroid gland, there are still multicentric findings and the presence of microscopic cancer does not 100% exclude residual tissues or the absence of lesions in the contralateral thyroid gland, and the residual thyroid tissues provide a breeding ground for possible recurrence in the future. 2. A small part of the retained thyroid tissue cannot meet the physiological needs of the whole body, and hypothyroidism occurs, with negative feedback to the pituitary gland, which will produce excessive thyroid stimulating hormone TSH, which promotes the growth of thyroid cancer tissue while promoting the recovery of thyroid tissue. Patients are often clinically given exogenous thyroid hormone for supplementation, and patients with total excision should definitely be supplemented with exogenous thyroid hormone, only the amount of supplementation is increased. Therefore, from the perspective of preserving thyroid function alone, it does not make much sense not to do total excision. 3. Because of the complexity of the anatomy around the thyroid gland, it is almost impossible to remove all the thyroid tissues without any residue because of the need to protect the surrounding nerves and parathyroid glands. In contrast, 131 iodine removal of residual thyroid tissue (familiarly known as “nail clearing”) is based on the principle of radioactive targeted therapy, which eliminates the need to consider the location, morphology and anatomical complexity of the thyroid gland, as long as the appropriate dose is used to completely remove the thyroid gland. 4. Since residual thyroid tissue produces thyroglobulin (Tg) and differentiated thyroid cancer can also produce a small amount (Tg), early recurrence and metastasis of thyroid cancer cannot be promptly diagnosed by blood chemistry. By removing the normal thyroid tissue that produces Tg through surgery + 131 iodine, monitoring Tg in blood can become the only meaningful and sensitive indicator to monitor the recurrence or metastasis of thyroid cancer, and by detecting Tg level in blood, we can know whether the differentiated thyroid cancer is recurring or metastatic in time. 5.131 iodine is a kind of radioactive iodine, which is mainly collected in the body with thyroid gland and other tissues that take in iodine. Since differentiated thyroid cancer cells are better differentiated, they have the ability to partially take up iodine, but usually much weaker than thyroid tissue. When normal thyroid tissue is removed, well differentiated thyroid cancer tissue can take up a certain amount of 131 iodine. By giving a diagnostic dose of 131 iodine whole body scan, it can screen for tumor recurrence and metastasis in other organs of the body, which is an important part of postoperative follow-up. 6.After the removal of thyroid tissue, if the relevant indicators suggest recurrence or metastasis, a therapeutic dose of 131 iodine is given to destroy the tumor cells by using the beta rays emitted from its decay to treat metastatic foci of differentiated thyroid cancer. Therefore, it is also called “internal radiotherapy”.