CEACAM5 and medullary thyroid gland carcinoma: Carcinoembryonic antigen (CEA), an adhesion glycoprotein expressed by neuroendocrine cells, is commonly used in MTC mainly in progressive disease, although it can be elevated also in several other types of cancer and also in many physiopathological conditions including tobacco smoking, gastrointestinal tract inflammatory disease and benign lung disease [11].