Adrenocorticotropic hormone--secreting islet cell tumors: are they always malignant?

To evaluate the frequency with which benign occult islet cell tumors cause ectopic adrenocorticotropic hormone (ACTH) syndrome.Ten patients with Cushing syndrome due to the production of ACTH by a pancreatic islet cell tumor were studied. In addition, 53 cases of ACTH-secreting islet cell tumors in the English-language literature were reviewed.All 10 of the authors' patients had malignant islet cell tumors. Liver metastases were present in all 10 patients at presentation. Five patients are dead, four patients are alive with liver metastases, and one patient is alive without gross evidence of residual tumor after distal pancreatectomy and right hepatectomy. Eight of the 10 islet cell carcinomas produced gastrin in addition to ACTH. In the 53 reported cases of ectopic ACTH production, there was only one benign adenoma with a prolonged follow-up.When ectopic ACTH production is caused by an islet cell tumor, the tumor is large and malignant and has usually metastasized to the liver by the time Cushing syndrome is diagnosed. No occult ACTH-producing islet cell tumor was encountered in the authors' experience or in a review of the literature.