Indeed, if thyroid function assessed by the measurement of free triiodothyronine (fT3), free thyroxine (fT4) and thyroid stimulating hormone (TSH) is usually in the normal range, the presence of elevated values of serum CTN, and CEA particularly in advanced cases, sometimes represents the first suspicion of the MTC, thus requiring further diagnostic procedures (31). The gene discussed is CEACAM5; the disease is medullary thyroid gland carcinoma.