Malignant tumors of the thyroid gland include papillary thyroid cancer, follicular thyroid cancer, medullary thyroid cancer, undifferentiated thyroid cancer, and malignant lymphoma. The nature of these tumors varies greatly, and thus the degree of malignancy also varies greatly. However, thyroid tumors have a less than 2% incidence of malignancy. Despite being defined as malignant, most of the time, it only progresses slowly between five and ten years. Because it is easily detected at an early stage and most of them can be cured with proper treatment, one should not panic even if told that it is malignant and should be treated with peace of mind. Malignant tumors are basically papillary thyroid cancer 85% of the malignant tumors of the thyroid are papillary thyroid cancer. This tumor is a follicular carcinoma that bulges out like a nipple. Papillary thyroid cancer develops very slowly, but in the process, it squeezes the surrounding tissues, so patients may feel compression of the esophagus, trachea, and nerves. Moreover, like undifferentiated thyroid cancer described below, it has an express progression and suddenly becomes seriously ill. In addition, papillary thyroid cancer is characterized by metastasis to adjacent lymph nodes. In summary, although most papillary thyroid cancers develop slowly and are easily treated, it is essential to choose the appropriate treatment modality. Follicular thyroid carcinoma, which is also follicular, accounts for 5% to 10% of thyroid malignancies. Follicular thyroid cancer is characterized by metastasis to adjacent lymph nodes, as well as metastasis to isolated bones and lungs. Such metastases sometimes occur in advanced stages of the disease. Medullary thyroid carcinoma, an unusual type of malignancy The so-called follicles, which are tissues formed as a result of thyroid hormone secretion, have many follicular cells concentrated together, with the presence of a few substances called parafollicular cells (C cells). These C cells secrete calcitonin. Calcitonin is a hormone that causes a decrease in the concentration of calcium in the blood. Medullary thyroid cancer is a malignant tumor that grows on these C cells. Many cases run in families, and some are spontaneous. Because it has metastases to the skull and lungs, it is in a slightly more malignant position than papillary thyroid cancer and follicular thyroid cancer and slightly less malignant than undifferentiated thyroid cancer. However, its incidence is very low, accounting for only 1%-2% of thyroid malignancies. Undifferentiated thyroid cancer with high risk Undifferentiated thyroid cancer is the most malignant and most rapidly developing of all thyroid malignancies. There are no good treatment options for undifferentiated thyroid cancer and it can be said that the mortality rate is high whenever the disease is present. However, its incidence rate is only about 1% of thyroid malignant tumors, so it can be said that the incidence rate is extremely low.