Medullary thyroid carcinoma is characterized very clearly by two types, one is called derivative and one is familial. Especially some of our familial ones, that is, they are clearly hereditary. Some patients have a medullary carcinoma in their family, and it is very likely that their family members will have medullary carcinoma, and we can find out these patients through genetic testing at a very early age. Secondly, medullary thyroid cancer has a distinctive feature that some patients will have some hormonal reactions, such as flushing, panic and diarrhea. Therefore, for patients with thyroid tumor and persistent diarrhea, this diarrhea cannot be cured by general treatment. This patient should be highly suspected of medullary thyroid cancer, which is a very obvious feature. Of course, general examination, general ultrasound and CT may not be very different from papillary thyroid cancer and follicular carcinoma. However, clinically, it does have very obvious characteristics based on the symptoms. There is also a laboratory test result for medullary thyroid carcinoma. If we suspect medullary thyroid carcinoma, we must check his hepatocrit, which can be very high in this patient. All patients with family history or suspected medullary thyroid cancer are generally recommended to have these two tests.