68 Ga-NODAGA-EXENDIN-4 PET/CT in the Detection or the Exclusion of Occult Sporadic Insulinomas

The diagnosis and localization of insulinomas remain challenging. Imaging with contrast-enhanced CT, PET with somatostatin analogs, MRI, and endoscopic ultrasonography is often inconclusive. GLP1 receptor radioligands can specifically target insulinomas. A recent multicenter trial reported the superior performance of 68 Ga-NODAGA-Exendin-4 (EX) PET/CT for the detection of benign insulinomas.

Fifty EX-PET/CTs (individually authorized by the French Medicine Agency) were performed on 44 patients with a suspected sporadic insulinoma, based on biochemistry and clinical signs, but without a target lesion identified by imaging. A composite reference standard was based on postsurgical histology and/or follow-up data over 6-45 months after the EX-PET/CT.

The examination-based EX-PET/CT positivity rate was 62% (31/50), equivocal 0. Positive EX-PET/CTs were confirmed by the outcomes of all 29 EX-guided resections (PPV 100%), including 2 re-operations following partial resection. Furthermore, the suspected diagnosis of an insulinoma was abandoned in 12 patients after 14 of 19 negative EX-PET/CTs. Suspicion of occult insulinoma remained in 5 patients. EX-PET/CT performed similarly well in patients treated by antihypoglycemic drugs and/or younger than 18 years. Since no extra-pancreatic EX abnormal foci were observed, the EX-PET/CT field-of-view to the upper abdomen should be sufficient. Only 1 patient experienced symptomatic hypoglycemia after EX injection.

In cases of suspected insulinomas with nondiagnostic imaging, the performance of EX-PET/CT for the detection of nonmalignant sporadic insulinomas was excellent, with a 29/50 (58%) rate of major impact on patients' management. A negative EX-PET/CT appears to be a confident predictor to rule out the presence of sporadic insulinoma.