SUN-633 Giant Insulinoma: A Rare Cause of Recurrent Hypoglycemia

Abstract Disclosure: W. Wang: None. Y. Bee: None. Background: Insulinomas are pancreatic neuroendocrine tumours with an incidence of 1-4 cases per million individuals annually1, and typically measure less than 3cm in diameter. Giant insulinomas, exceeding 9cm in diameter, are exceedingly rare with fewer than 50 reported cases in literature.2 Clinical Case: A 58-year-old male with no history of diabetes mellitus presented with recurrent episodes of neuroglycopenic symptoms. Biochemical evaluation during a supervised fast was consistent with endogenous hyperinsulinism - blood glucose 2.7mmol/L, C-peptide 7.08ug/L (0.78-5.19ug/L), Insulin 32.6mU/L (1.0-30.0mU/L), Pro-insulin 161pmol/L (3.6-22pmol/L0, Ketones 0.1mmol/L (0.0-0.6mmo/L). Computed tomography of the abdomen and pelvis revealed a 13x11x12cm hypervascular mass at the pancreatic tail. Chromogranin A was elevated 947ug/L (<102ug/L)). Continuous glucose monitoring was utilized to monitor hypoglycemia while awaiting surgical resection. Open subtotal pancreatosplenectomy and cholecystectomy was performed, and histopathological analysis confirmed G3 well-differentiated neuroendocrine tumour. The patient developed hyperglycemia post-operatively and insulin glargine once daily was started. There was no evidence of disease recurrence nor metastases at the 3-month follow up mark. Conclusion: While insulinomas are typically benign, giant insulinomas have higher likelihood of malignancy and rates of invasiveness. Close surveillance with monitoring of symptoms, blood glucose and chromogranin A levels and interval imaging is required to detect recurrence and/or metastases. References:1 Hofland J, Refardt JC, Feelders RA, Christ E, de Herder WW. Approach to the Patient: Insulinoma. J Clin Endocrinol Metab. 2024;109(4):1109-1118. doi:10.1210/clinem/dgad6412 Tarris G, Rouland A, Guillen K, et al. Case Report: Giant insulinoma, a very rare tumor causing hypoglycemia. Front Endocrinol (Lausanne). 2023;14:1125772. doi:10.3389/fendo.2023.1125772 Presentation: Sunday, July 13, 2025