Gastrinomas are neuroendocrine tumors (NETs), usually located in the duodenum or pancreas, that secrete gastrin and cause a clinical syndrome known as Zollinger–Ellison syndrome (ZES). A large number of gastrinomas develop in the pancreas or duodenum, with near-equal frequency, and approximately 10% arise as primary neoplasms in lymph nodes of the pancreaticoduodenal region (gastrinoma triangle). Most gastrinomas are sporadic (75–80%), whereas approximately 20–25% are associated with multiple endocrine neoplasia type 1 (MEN-1). Over 50% of gastrinomas are malignant and can metastasize to regional lymph nodes and liver. One fourth of gastrinomas are related to multiple endocrine neoplasia type 1, Zollinger–Ellison syndrome, peptic ulcer disease. Signs and symptoms Gastrinoma in the early stages will have signs and symptoms of indigestion or similar to irritable bowel disease (IBD) such as: Hypergastrinemia Refractory or recurrent peptic ulcers involving duodenum Chronic diarrhea Generalized cancer symptoms Abdominal pain Gastrointestinal bleeding Obstruction of intestine Weight loss/poor appetite Anemia (Due to vitamin B12 malabsorption, and bleeding) Hematemesis Gastroesophageal reflux disease Esophageal complications (Barrett's esophagus, esophagitis, stricture formation) Vomiting Steatorrhea Pathophysiology Gastrin is secreted by the G cells. G cells are primarily found in the pyloric antrum but can also be found in the duodenum and the pancreas. The primary function of gastrin is to induce the release of hydrochloric acid (HCl) from the parietal cells located in the fundus of the stomach. Parietal cells are responsible for hydrochloric (HCl) secretion along with intrinsic factor that binds to vitamin B12 and helps with its uptake in the terminal ileum. Other functions of gastrin include stimulating the growth of gastric mucosa and gastric motility and promoting gastric emptying. These mechanisms of the gastrointestinal tract (GIT) are up-regulated by the vagus nerve of the parasympathetic nervous system (PNS), which carries out the majority of its functions by the release of neurotransmitter Acetylcholine (Ach), and to a lesser extent gastrin releasing peptide (GRP) protein. On the contrary, the functions of GIT are down-regulated by the activation sympathetic nervous system (SNS), which carries out its functions mostly via neurotransmitter epinephrine. Meal consumption causes distention of the stomach, leading to stimulation of the parasympathetic vagus nerve in the gastric mucosa, which causes the release of GRP protein. In gastrinoma, GRP protein causes larger than normal amounts of gastrin secretion, which leads to hyperplasia of the parietal cells. Hyperplasia of parietal cells causes an abnormal release of HCl into the duodenum, which causes the