Our data showed that the expression levels of serum Ctn, CEA, and NSE in MTC patients with LLNM (Group LLNM) were significantly higher than those without LLNM (Group non‐LLNM), whereas the levels of serum AFP, CYFRA21‐1, CA19‐9, and CA242 had no statistical difference between these two groups. This evidence concerns the gene CEACAM5 and medullary thyroid gland carcinoma.