A noninvasive way to identify the exact position of very small insulinomas — life-threatening pancreatic tumors — will allow surgeons to successfully remove growths as small as 1 cm in diameter. Insulinomas are very rare, with an incidence of between two and four cases per million people a year. They secrete insulin in an unregulated way, causing blood glucose to fall lower than normal. “In the majority of cases, these tumors are benign, but they are life-threatening because they can lead to severe hypoglycemia — low blood glucose,” said professor Emanuel Christ, an endocrinologist at the University Hospital of Bern. Christ and his research team observed that a particular type of receptor is present on the cell surface of insulinomas, which can be targeted with a radioactively labeled drug. They developed a technique that scans patients with single-photon emission computed tomography (SPECT) combined with conventional CT to detect where the drug has bound to insulinoma cells. They precisely localized tumors as small as 1 cm in diameter. “These data suggest that it’s possible to detect very small, life-threatening insulinomas within the pancreas, based on the characteristic receptors on the surface of these tumors,” Christ said. “This technique avoids the more invasive tests to localize the insulinomas and facilitates the surgical approach. Surgery is still the only method of curing this particular disease.” Thirty patients (18 men, 12 women) were injected with the drug. Following the injection, scans were conducted after 30 minutes, and after 4, 23, 96 and up to 168 hours. SPECT imaging with 111In-exendin-4 correctly detected 23 benign insulinomas, one malignant tumor, two islet hyperplasia and two uncharacterized lesions. Conventional MRI, CT and endosonography detected the tumors in 17 patients. No false negative results occurred. The technique also detected another malignant insulinoma and an islet hyperplasia. The positive predictive value of the test was 85 percent, and the negative predictive value was 100 percent. The tumors were surgically removed after the scans. The tissues were examined to confirm diagnosis. Small insulinomas currently are detected invasively using various techniques, including a process known as arterial stimulation with venous sampling, which involves injecting calcium gluconate into the arteries supplying the pancreas and taking samples from veins to test for insulin. Christ and his team are now working to see whether positron emission tomography could be more effective for tumor localization. The observations were presented May 7 at the joint International Congress of Endocrinology/European Congress of Endocrinology. For more information, visit: www.insel.ch/en/