Thyroid cancer accounts for about 1% of all cancers. In endemic areas with endemic nodular goiter, the incidence of thyroid cancer, especially hypofractionated thyroid cancer, is also high. The incidence rate of thyroid cancer is higher in females, with a ratio of 1:2.58. In terms of age, it can occur from children to the elderly, but unlike the common feature of cancer occurring in the elderly, thyroid cancer occurs more often in young adults, with an average age of about 40 years. The age distribution of various types of thyroid cancer varies. Papillary carcinoma is the most widely distributed and can occur in children under 10 years old to 100 years old, follicular carcinoma in 20-100 years old, medullary carcinoma in 40-80 years old, and undifferentiated carcinoma in 40-90 years old. The specific etiology of thyroid cancer is still difficult to be sure, but from epidemiological surveys, experimental tumor studies and clinical observations. The occurrence of thyroid cancer may be related to the following factors. 1.Radiation damage to the thyroid gland of experimental rats with X-rays can induce the development of thyroid cancer in animals. It is proved that 131Ⅰ can change the metabolism of thyroid cells, the nucleus is deformed and the synthesis of thyroxine is greatly reduced. It can be seen that on the one hand, radiation causes abnormal division of thyroid cells, leading to cancer; on the other hand, it destroys the thyroid gland and cannot produce endocrine hormone, and the resulting large secretion of thyroid stimulating hormone (TSH) can also promote thyroid cell carcinogenesis. In clinical practice, many facts indicate that thyroid gland development is related to the action of radiation. Of particular interest is the fact that children who have been treated with radiation to the upper mediastinum or neck during infancy for thyroid enlargement or lymphoglandular proliferation are particularly susceptible to thyroid cancer, because the cells of children and adolescents are highly proliferative and radiation is an additional stimulus for tumor formation. In adults, thyroid cancer is less likely to occur after neck radiation therapy. 2. Excessive iodine and TSH intake or iodine deficiency can change the structure and function of the thyroid gland. For example, the incidence of thyroid cancer in endemic areas of Switzerland is 20 times higher than that of non-endemic areas such as Berlin at 2 per 1,000. Conversely, a diet high in iodine also predisposes to thyroid cancer. Iceland and Japan, the countries with the highest iodine intake, have higher rates of thyroid cancer detection than other countries. This may be related to the factor of TSH stimulating thyroid hyperplasia. Experiments have shown that long-term TSH stimulation can contribute to thyroid hyperplasia, nodule formation and cancerous changes. 3. Other thyroid lesions have been reported clinically as thyroid adenocarcinoma, chronic thyroiditis, nodular goiter or some toxic goiter, but the relationship between these thyroid lesions and thyroid cancer is not yet certain. For example, most of thyroid adenomas are follicular type and only 2-5% are papillary; if thyroid cancer is transformed from adenoma, most of them should be follicular type, but in fact, more than half of thyroid cancers are papillary cancers, so it is presumed that the incidence of thyroid adenoma carcinoma is very small. About 5-10% of medullary thyroid carcinomas have obvious family history and are often combined with pheochromocytoma, so it is presumed that the occurrence of such carcinomas may be related to chromosomal genetic factors.