The CCK2 receptor is (over)expressed in several tumor types, including NENs, such as medullary thyroid cancer (MTC) and gastro-entero-pancreatic tumors, but also small cell lung cancer (SCLC), astrocytomas, stromal ovarian cancer, breast, endometrial and ovarian adenocarcinomas [91,92]. This evidence concerns the gene CCKBR and medullary thyroid gland carcinoma.