The area under the curve (AUC) predicted by serum Ctn, CEA, and NSE for LLNM in MTC patients was 0.867, 0.831, and 0.726, respectively, and the AUC of serum Ctn, CEA, and NSE combined detection was up to 0.890, higher than using a single biomarker. This evidence concerns the gene CEACAM5 and medullary thyroid gland carcinoma.