6799 RZ358 Therapy. A Novel Approach To Hyperinsulinemia In Metastatic Neuroendocrine Tumor Patients

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Abstract Disclosure: J. Noreña: None. T. Akcan: None. S. Patel: None. W. Madeleine: None. S. Shaheen: None. M. Tan: None. RZ358, an intravenously administered monoclonal antibody, targets a unique allosteric site on the insulin receptor. It is under investigation for hypoglycemia due to congenital hyperinsulinism. We present a case of its efficacy in treating refractory hyperinsulinemic-hypoglycemia (HH) due to a metastatic pancreatic neuroendocrine tumor (pNET). Clinical Case: A 50-year-old woman with a 6-year history of HH initially presented in 2016 with epigastric pain and was diagnosed with gastrin secreting pNET pT3N1. After Whipple surgery and cholecystectomy. A well-differentiated, WHO grade 2 NET, positive in immunohistochemistry for AE1/3, synaptophysin and Ki-67 index of 9.2% was confirmed. She presented recurrent disease with liver metastasis requiring somatostatin analogue Lanreotide. Subsequently despite Lanreotide, hypoglycemia persisted, and 72-hour fast confirmed HH. DOTATATE scan showed progression to new liver lesions. Everolimus was started and subsequently peptide receptor radionuclide therapy (PRRT) with fair hypoglycemia control. Unfortunately, her disease progressed. Oral glucose, cornstarch, and diazoxide failed. After a left hepatectomy and transarterial chemoembolization, her severe hypoglycemia improved briefly. Despite high-dose dexamethasone (up to 4 mg daily), octreotide 400 mcg every 8 hours, and high-calorie total parenteral nutrition (TPN) (over 800 grams of carbohydrates daily), she required multiple hospitalizations for persistent symptomatic hypoglycemia. Moreover, these therapies led to significant side effects, including recurrent episodes of volume overload, 240 pounds weight gain over a year, and Cushingoid features. Given RZ358's reports in reversing HH in rodents, humans, and a recent report of successful use in a malignant insulinoma case, we aimed to start RZ358 in our patient. We obtained, emergency use authorization from the FDA, IRB of Stanford University School of Medicine approval, and patient written informed consent. RZ358 was started at 6 mg/kg biweekly, along with octreotide, dexamethasone, and TPN. RZ358 dosage was later increased to 9 mg/kg weekly, allowing a substantial reduction in dexamethasone to physiological doses and a 50% reduction in TPN carbohydrate requirements. She achieved normoglycemia and returned home, but missing a single weekly RZ358 dose caused recurrent severe hypoglycemia until the next dose administration.As her disease progressed, the patient opted for comfort care, discontinuing TPN and RZ358. Conclusion: RZ358 represents a novel and unique treatment option for refractory HH in patients with metastatic NETs and can improve clinical outcomes when standard interventions fail. This case underscores the potential of RZ358, a monoclonal antibody, to treat HH beyond its approved use for congenital cases, suggesting its applicability to cases of hyperinsulinemia secondary to NETs in adults. Presentation: 6/2/2024