Medullary thyroid carcinoma is a neuroendocrine tumor and the most significant clinical feature is the elevation of calcitonin and carcino‐embryonic antigen (CEA).24, 25 Calcitonin and CEA are the most valuable tumor markers of MTC, and serum concentration of them is directly related to the number of c‐cells. Here, CEACAM5 is linked to neoplasm.