GCG and neoplasm: Thus, tumor types range from histamine-secreting gastric ‘carcinoids’ to a mélange of pancreatic lesions (secreting glucagon, insulin, somatostatin, or vasoactive polypeptide – colloquially known as islet cell tumors), as well as small intestinal ‘carcinoids’ (secretin, serotonin, and a variety of tachykinins) and colorectal lesions (enteroglucagon, GLP1, and pancreatic polypeptide (PP)).