CEACAM5 and medullary thyroid gland carcinoma: Compared with differentiated thyroid carcinoma, MTC appears to be more prone to cervical lymph node metastasis and distant metastasis and may be associated with many other factors in addition to tumor diameters, such as male sex, calcitonin, and carcinoembryonic antigen levels, RET mutations, bilateral carcinoma, multifocal carcinoma, neoplasmic thyroid extracapsular invasion, marginal burrs, morphological irregularities, calcification, and blood supply (26–31).