1.Radiation damage (19%): irradiating the thyroid gland of laboratory rats with X-rays can prompt the development of thyroid cancer in animals. The occurrence of thyroid gland is related to the action of radiation. It is particularly noteworthy that children who have received radiation treatment to the upper mediastinum or neck during infancy due to enlarged thymus or lymphadenopathy are particularly susceptible to thyroid cancer, because the cells of children and adolescents are proliferating vigorously and radiation is an additional stimulus to promote the formation of their tumors. In adults, the chance of thyroid cancer occurring after neck radiation therapy is uncommon. 2. Iodine deficiency (25%): Excessive iodine and TSH intake or iodine deficiency can change the structure and function of 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 (20%): There are clinical reports of thyroid adenocarcinoma, chronic thyroiditis, nodular goiter or certain toxic goiters becoming cancerous, 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 papilloma; if thyroid cancer is transformed from adenoma, most of them should be follicular type, but in fact, more than half of thyroid cancers are cephalic carcinoma, so it is presumed that the incidence of thyroid adenoma carcinoma is also small. Genetic factors (10%): About 5-10% of medullary thyroid carcinomas have obvious family history and are often combined with pheochromocytoma and other intercalation, so it is presumed that the occurrence of these carcinomas may be related to chromosomal genetic factors. Familial factors and thyroid cancer Thyroid cancer is rarely seen as an independent familial syndrome, but can be part of a familial syndrome or hereditary disease. A few families have a tendency to develop multifocal well-differentiated thyroid cancer. Thyroid cancer is associated with familial colonic polyposis (e.g. Gardner’s syndrome), including colonic adenomatous polyps combined with soft tissue, most often with fibromatosis, combined with fibrosarcoma, an autosomal dominant disease. autosomal dominant disorder, caused by mutations in the APC gene located on chromosome 5q21 to q22, the latter being a signaling protein involved in the regulation of cell proliferation, and in a minority of individuals, thyroid cancer can occur under TSH stimulation.