Glucagon-Like Peptide-1 Versus Somatostatin Receptor Targeting Reveals 2 Distinct Forms of Malignant Insulinomas

Glucagon-like peptide-1 (GLP-1) receptor imaging is superior to somatostatin receptor subtype 2 (sst(2)) imaging in localizing benign insulinomas. Here, the role of GLP-1 and sst(2) receptor imaging in the management of malignant insulinoma patients was investigated. Methods: Eleven patients with malignant insulinoma were prospectively included. (111)In-[Lys(40)(Ahx-diethylenetriaminepentaacetic acid [DTPA])NH(2)]-exendin-4 SPECT/CT, (68)Ga- DOTATATE PET/CT, and in vitro receptor autoradiography were performed to assess the receptor status and to evaluate the detection rate. Results: GLP-1 receptor targeting was positive in 4 of 11 patients, and sst(2) receptor expression was positive in 8 of 11. In only 1 patient were both receptors expressed. In 1 patient, GLP-1 receptor imaging was the only method that successfully localized the primary tumor in the pancreas. In 3 patients with sst(2)-expressing tumors, DOTATATE radiotherapy was effectively applied. Conclusion: As opposed to benign insulinomas, malignant insulinomas often lack GLP-1 receptors. Conversely, malignant insulinomas often express sst(2), which can be targeted therapeutically.