ABSTRACT
In patients with medullary thyroid carcinoma (MTC), calcitonin (Ctn) and carcinoembryonic antigen (CEA) were the most important serum biomarkers for diagnosis, evaluation and follow-up. Approximately 0.3% to 5.9% of the thyroid nodule population could present with elevated Ctn on screening, and a diagnosis of MTC can be basically confirmed when serum Ctn > 100 pg/ml.. Ctn and CEA levels could reflect tumor burden and help determine the extent and timing of surgery. When preoperative serum Ctn >200 pg/mL or CEA >30 ng/mL, nearly more than one-third of patients had lateral neck lymph node metastasis. Few patients developed distant metastasis when Ctn<500 pg/mL, however the proportion of distant metastasis could reach 75% when CEA>100 ng/mL. In inherited MTC patients, tumors with Ctn<30 pg/mL were usually localized in the gland without metastasis. The time to normalization of serum Ctn and CEA postoperatively was one month in most patients. According to the response to initial therapy, patients with undetectable Ctn and normal CEA had a low risk of relapse and death in the follow-up period. The risk of local recurrence, LNM and distant metastasis increased as Ctn levels rose. The Ctn/CEA doubling time could predict the disease prognosis, and when it was less than 0.5 years, most patients would die.