Medullary thyroid carcinoma (MTC) is a highly malignant disease, between differentiated thyroid carcinoma and undifferentiated carcinoma, prone to lymphatic metastases (neck and mediastinum) and distant metastases through blood vessels, making it difficult to treat. It originates from the parafollicular cells of thyroid gland. Surgery is the first and main treatment for medullary thyroid carcinoma, and endocrine therapy and I131 therapy are not effective, but radiotherapy, biologic targeted therapy and supportive therapy can be considered for those without surgical indication. The 10-year survival rate for patients with regional lymph node metastasis is about 75%, and the 10-year survival rate for patients with distant metastasis is about 40%. In China, the incidence of medullary thyroid cancer is low. Patients unfortunately suffering from medullary thyroid cancer, if there is no contraindication, surgery is necessary. In addition to routine tests, preoperative tests such as calcitonin and CEA, RET mutation test if necessary, and other tests are needed to assess the presence of cervical and thoracic lymph nodes and distant organ metastases. In most cases, the diagnosis of medullary thyroid cancer relies on laboratory tests for calcitonin and carcinoembryonic antigen, and the diagnosis is confirmed by pathological examination. For patients with suspected medullary thyroid cancer, they can be used as routine laboratory tests. In general, calcitonin and carcinoembryonic antigen are elevated in patients with medullary thyroid cancer before treatment, and they both decrease significantly and progressively after treatment, so calcitonin and carcinoembryonic antigen measurements (especially calcitonin) can be used as indicators for medullary thyroid cancer diagnosis and postoperative treatment follow-up. If postoperative calcitonin and carcinoembryonic antigen levels fall to normal or remain low, the tumor is generally considered to be completely removed. Of course, they do not fall at a consistent rate, and will generally fall to their lowest levels 1 month after treatment. If calcitonin and or carcinoembryonic antigen levels rise after treatment, especially progressively, this suggests that the tumor is difficult to remove completely or that the tumor has recurred. When interpreting the results of calcitonin and carcinoembryonic antigen measurements, physicians and patients should not simply look at their absolute values; what is important is the trend of their changes and the magnitude of their increase. It is important to note that increased carcinoembryonic antigen should also be considered for other neoplastic diseases, as it is not very specific in medullary thyroid carcinoma.