GLP1R and gastrin-producing neuroendocrine tumor: Research in molecular targeting of GLP-1R expressed on beta cells 43 and involved in various pathological processes, e.g. in insulinomas, gastrinomas, and phaeochromocytomas 23, 32, 33, 41 has been expanding very fast since the development of metabolically stable ligands, e.g. exendin-4.