In conclusion, the present data can allow to report that (1) Ctn remains the most reliable tool to diagnose MTC, (2) CEA doubling time is essential during the postoperative follow-up to identify patients at high risk of death, (3) US features, and TIRADSs, are not sufficiently reliable to diagnose MTC, (4) cytological examination has poor sensitivity in detecting MTC and FNA-Ctn is essential to avoid false negative biopsy, and (5) PET/CT (in particular using [18F]FDOPA as radiopharmaceutical) is useful for detecting recurrent MTC. The gene discussed is CEACAM5; the disease is medullary thyroid gland carcinoma.