Cholecystokinin-2 receptor (CCK2R), a member of the G-protein coupled receptor (GPCR) family, is a membrane-bound transmembrane protein that is highly expressed in various neuroendocrine tumors (NETs), including those of small cell lung cancer (SCLC), and medullary thyroid carcinoma (MTC), while exhibiting low expression in most normal tissues 1-4. This evidence concerns the gene CCKBR and medullary thyroid gland carcinoma.