In particular, medullary thyroid carcinoma (MTC) has high CEA levels, and CEA measurement is key to the diagnosis of MTC [13]. According to the guidelines of the North American Society for Neuroendocrine Tumors, preoperative levels > 30 ng/mL indicate that the disease has spread beyond the thyroid gland [14]. This evidence concerns the gene CEACAM5 and neuroendocrine neoplasm.