GLP1R and gastrin-producing neuroendocrine tumor: GLP-1R is highly expressed on insulinomas, gastrinomas, phaeochromocytomas, and other neuroendocrine tumors [1,5], and [Lys40(Ahx-DTPA-111In)NH2]-exendin-4, a radiolabelled GLP-1 analogue, is specifically internalized in GLP-1R-expressing tumor cells [6,7].