GAST and neoplasm: There are a number of substances that are secreted alone or in combination by these neoplasms, including 5-serotonin (5-HT), 5- hydroxytryptophan (5-HTP), kallikrein, adrenocorticotropic hormone (ACTH), histamine, P substance, prostaglandin, catecholamines and gastrin.12,13 These vasoactive substances produced by tumor cells cause carcinoid syndrome that presents with vasomotor flushing, episodic hypotension and diarrhea.