Thyroid cancer is a disease of the thyroid gland in which tumor (malignant) cells are found in the thyroid tissue. Adenocarcinoma accounts for the majority of malignant tumors of the thyroid gland, while only 1% of malignant tumors originate in the interstitial thyroid gland. Thyroid cancer accounts for about 1.5% of all cancers in the body and 2.7% to 17.0% of all tumors of the thyroid gland. According to the statistics of International Cancer Society, the incidence of thyroid cancer is increasing year by year in different countries. In China, the incidence rate of thyroid cancer in Shanghai was 1.02/100,000 in 1960, 2.39/100,000 in 1972 and 3.80/100,000 in 1978. According to the statistics of Zhongshan and Huashan Hospitals affiliated to Shanghai Medical University, the two hospitals treated 6432 cases of thyroid disorders from 1975 to 1985, including 4363 cases of thyroid tumors and 435 cases of thyroid cancer, accounting for 10.1% of all thyroid tumors. In the United States, about 18,000 people are diagnosed with thyroid cancer each year, and about 1,200 of them die from this disease. The number of women with thyroid cancer is two to four times higher than that of men, and the reasons for this difference are not known. The most common age of onset is 25 to 65 years.