GCG and pancreatic neuroendocrine tumor: Pancreatic endocrine tumors are usually well differentiated and classified as functional or nonfunctional based on their ability to secrete hormones.7 Functional tumors secrete hormones including insulin, glucagon, vasoactive intestinal peptide, somatostatin, and rarely neurotensin, growth hormone–releasing factor, and adrenocorticotropic hormone.