CEACAM5 and medullary thyroid gland carcinoma: In MTC patients, preoperative serum levels of CEA and Ctn display various patterns of alteration, which can be broadly classified into four categories: 1) Concurrent elevation of both CEA and Ctn; 2) Elevated Ctn with normal CEA; 3) Elevated CEA with normal Ctn; and 4) Normal levels of both biomarkers.