Glucagon-like Peptide 1–Receptor Scans to Localize Occult Insulinomas

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Abstract
The precise localization of some insulinomas (islet-cell adenomas that secrete insulin) with the use of conventional imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), endosonography,1 and indium-111 (111In)–labeled pentetreotide scintigraphy (OctreoScan),2 is a challenging clinical problem. In vitro studies have demonstrated that receptors for glucagon-like peptide 1 (GLP-1) are highly overexpressed in almost all insulinomas.3,4 Therefore, GLP-1-like radioligands retaining high binding affinity to GLP-1 receptors have been developed. One such radioligand, [Lys40(Ahx-DTPA-111In)NH2]exendin-4, successfully targeted insulinomas in the Rip1-Tag2 mouse.5 We evaluated the diagnostic value of GLP-1–receptor scintigraphy in two patients with insulinomas that either were not localized (Patient 1) or were unsatisfactorily localized (Patient 2) with the use of conventional imaging methods.