THU526 Long-term Follow-up Of A Functional Gastroenteropancreatic Tumor Secreting Both Somatostatin And Gastrin

Disclosure: R. Zafar: None. J. Syeda: None. K. Rajamani: None. Introduction: There have been fewer than 200 cases of somatostatinoma reported since 1977. We report a case of a functional Gastroenteropancreatic neuroendocrine tumor (GEP-NET) secreting both somatostatin and gastrin. Clinical Case: A 55-year-old male with diabetes mellitus, chronic diarrhea, gastric ulcer, and cholelithiasis was referred to the endocrinology clinic for poorly controlled diabetes mellitus. He had a history of B-cell lymphoma of the thyroid treated by chemotherapy and radiation. He was found to have two paraduodenal masses by PET CT scan during surveillance for recurrence of lymphoma. Laboratory evaluation revealed elevated levels of insulin, glucagon, gastrin, somatostatin, and chromogranin A on multiple occasions both fasting and random. Ultrasound-guided endoscopic biopsy of the paraduodenal nodules was initially read as a neuroendocrine tumor. Subsequent immunohistochemical staining was positive for both somatostatin and gastrin. The stains were negative for glucagon and insulin. The Ki-67 proliferation index was less than 1%. The patient declined surgical treatment of the paraduodenal tumors. He underwent cholecystectomy for cholelithiasis. Gastric ulcers resolved with the use of proton pump inhibitors. His blood glucose was well controlled with insulin. Sequential CT/PET scans showed no change in the size of paraduodenal masses over a follow-up period of 14 years. Conclusion: GEP-NETs may secrete more than one type of hormone simultaneously. This case highlights a functional GEP-NET with clinical manifestations due to elevated levels of somatostatin and gastrin. Characterization of GEP-NETs by immuno-histochemical staining and hormonal analysis may help direct clinical management. Although many GEP-NETs are managed surgically, this case suggests that the Ki-67 proliferation index and sequential PET or CT scans may guide the nonsurgical management of functional GEP-NETs. References: 1-Ganda OP et al. "Somatostatinoma": a somatostatin-containing tumor of the endocrine pancreas. N Engl J Med. 1977;296(17):963-7. 2-Hofland, J., Kaltsas, G., & de Herder, W. W. (2020). Advances in the diagnosis and management of well-differentiated neuroendocrine neoplasms. Endocrine Reviews, 41(2), 371-403. 3-M., Öberg, K., Falconi, M., Krenning, E. P., Sundin, A., Perren, A., & Berruti, A. (2020). Gastroenteropancreatic neuroendocrine neoplasms: ESMO Clinical Practice Guidelines for diagnosis, treatment, and follow-up. Annals of oncology, 31(7), 844-860.), 371-403. Presentation: Thursday, June 15, 2023