In addition to bCtn, serum carcinoembryonic antigen (CEA) levels are also associated with MTC risk, with CEA levels >30 ng/mL suggesting that the disease is unlikely to be cured with surgery, and CEA levels >100 ng/mL signifying extensive lymph node and distant metastases (63). This evidence concerns the gene CEACAM5 and medullary thyroid gland carcinoma.