The incidence of thyroid cancer varies greatly in different regions, although the disease varies in malignancy and develops more slowly compared to other organ cancers. It is worth noting that some primary foci are small and metastatic lesions are often found first clinically. There are mainly 4 types as follows. Papillary adenocarcinoma accounts for 40% to 60% of thyroid cancer, and is more common in adolescent females. It grows slowly and is mostly a 1 to 2 cm round mass without envelope when detected by the naked eye. The surface is gray or gray-brown, with some soft and some soft and hard texture. Microscopically, the cancer cells were arranged in a papillary pattern around a central axis of fibrovascular vessels, with more papillary branches. The cancer cells are rectangular or short columnar in shape, characterized by less chromatin in the nucleus, transparent or hairy glass-like, and no nucleoli. It may be accompanied by simple thyroid follicles, and sand granules are often found in the interstitium. About 50% of this cancer is found to have metastasis in the lymph nodes of the neck, and sometimes the primary foci are found after the metastatic foci, and some of the primary foci are even too small to be detected. The cancer is less malignant and the 5-year survival rate is 75%. Follicular adenocarcinoma accounts for 10%-15% of thyroid cancer, mostly found in women over 50 years old. The survival rate is 30% to 40% in 5 years after resection of the primary focus. To the naked eye, the tumor is grayish white, some are nodular with incomplete envelope, resembling adenoma; some are extensively infiltrated in the thyroid gland, and then invade the tracheal wall, neck blood vessels, muscles and laryngeal nerve. Microscopically, follicles of different degrees of differentiation can be seen. In well differentiated cases, the follicular structure is more regular and the cell heterogeneity is lower, so it is not easy to distinguish them from adenomas. In poorly differentiated cases, there are fewer follicles, irregular follicular morphology, some have solid cell nests, more obvious cell heterogeneity, and more nuclear fission images. In a few cases, this cancer is mainly composed of eosinophilic cells, so it is also called eosinophilic cell carcinoma. Undifferentiated carcinoma accounts for about 15% of thyroid cancer. It is highly malignant, fast growing and can infiltrate into surrounding tissues and metastasize at an early stage. Patients are mostly above 50 years old and there is no difference between men and women. It is grayish white in color, often with bleeding and necrosis. According to the histology, it can be divided into small cell type, giant cell type and spindle cell type. Small cell carcinoma consists of small round cells with diffuse distribution, which is quite similar to malignant lymphoma. If tumor cells show keratin (Keratin) or carcinoembryonic antigen (CEA), it can be identified as originating from epithelial tissue. The prognosis of giant cell carcinoma is the worst. Microscopic cancer cells vary in size and morphology, and there are often megakaryocytes and multinucleated giant cells. Medullary carcinoma is a carcinoma that occurs from parafollicular cells (also called C cells), accounting for 5% of thyroid cancer. Ninety percent of the tumors secrete calcitonin and some also secrete CEA, growth inhibitory hormone, prostaglandin and other hormones and substances, so the blood level of this hormone is increased, which is typical of multiple endocrine adenomas. To the naked eye, most disseminated cases start as a single mass, while familial cases are often multicentric. The tumor is yellowish-brown, soft, and clearly demarcated so that it appears to be enveloped at first glance. Microscopically, the tumor cells are round, polygonal or spindle-shaped cells arranged in clusters or cords, and occasionally small follicles are seen. The interstitium is rich, often with amyloid material and calcium salt deposits. Electron microscopically, the cytoplasm of tumor cells contained neuroendocrine granules 100-250 mm in diameter.