Context: The surgical removal of insulinomas is hampered by difficulties to localize it using conventional radiological procedures. Recently these tumors were shown to exhibit a very high density of glucagon-like peptide-1 receptors (GLP-1R) in vitro that may be used as specific targets for in vivo receptor radiolabeling.

Objective: The objective of the study was to test the 111In-labeled GLP-1R agonist 111In-DOTA-exendin-4 in localizing insulinomas using single photon emission computed tomography in combination with computed tomography images.

Design: This was a prospective open-label investigation.

Setting: The study was conducted at three tertiary referral centers in Switzerland.

Patients: Patients included six consecutive patients with proven clinical and biochemical endogenous hyperinsulinemic hypoglycemia.

Intervention: ¹¹¹In-DOTA-exendin-4 was administered iv at a dose of about 90 MBq (30 μg peptide) over 5 min. Whole-body planar images of the abdomen were performed at 20 min, 4 h, 23 h, 96 h, and up to 168 h after injection. After surgical removal of the insulinomas, GLP-1R expression was assessed in the tumor tissue in vitro by GLP-1R autoradiography.

Main Outcome Measure: The detection rate of insulinomas was measured.

Results: In all six cases, the GLP-1R scans successfully detected the insulinomas identified using conventional methods in four cases. By using a -probe intraoperatively, GLP-1R detection permitted a successful surgical removal of the tumors in all patients, diagnosed histopathologically as five pancreatic and one extrapancreatic insulinomas. In vitro GLP-1R autoradiography showed a high density of GLP-1R in all tested insulinomas.

Conclusion: In vivo GLP-1R imaging is an innovative, noninvasive diagnostic approach that successfully localizes small insulinomas pre- and intraoperatively and that may in the future affect the strategy of insulinoma localization.