Successful Control of Intractable Hypoglycemia Using Rapamycin in an 86-Year-Old Man with a Pancreatic Insulin-Secreting Islet Cell Tumor and Metastases

Context: Insulinomas are rare tumors of the pancreatic islet cells that produce insulin. Approximately 5 to 10% of these tumors are cancerous, and control of insulin secretion and hypoglycemia may be difficult in these patients. Malignant insulinomas generally respond poorly to traditional chemotherapeutic agent regimens. At present, streptozotocin is the only approved drug for the treatment of pancreatic islet cell tumors. Setting and Patient: This report describes a case of an elderly gentleman with a metastatic pancreatic insulinoma and severe hypoglycemia. A continuous infusion of octreotide lowered the blood glucose levels further. He required diazoxide, a thiazide diuretic, phenytoin, and a constant infusion of glucose to control the hypoglycemia and elevated insulin levels. Intervention: Rapamycin was administered at an oral dose of 2 mg/d. Results: On the mTOR (mammalian target of rapamycin) agent rapamycin, he was weaned off all drugs except for the thiazide diuretic and maintained euglycemia with a reduction of circulating insulin levels. He remained euglycemic for the past year with no evidence of tumor progression based on Octreoscan. His quality of life is excellent, and he remains active having recently completed a triathlon. Conclusions: Rapamycin may provide a useful means of abrogating tumor growth and controlling hypoglycemia in malignant insulinomas by reducing the malignant beta-cell growth and proliferation as well as inhibiting insulin production. (J Clin Endocrinol Metab 94: 3157-3162, 2009)