The purpose of this study is to determine the clinical importance of measuring preoperative and postoperative CEA values in patients with medullary thyroid carcinoma by studying the current literature, and to define the significance of the correlation between CEA and the origin of C cells, as well as to find possible new therapeutic interventions and targets using as a “tool” the detection of CEA in the body of patients with MTC. The gene discussed is CEACAM5; the disease is medullary thyroid gland carcinoma.