A gastrinoma is a tumour that secretes the hormone gastrin. Gastrin, produced by G cells in the antrum of the stomach, stimulates the parietal cells in the corpus of the stomach to produce acid. In normal physiology, this acid then inhibits the release of gastrin from the G cells in a process of negative feedback, as illustrated below.
The release of gastrin from the G cells - click to enlarge
The cells of the gastrinoma no longer respond to this negative feedback and a huge excess of acid is produced due to the production of large amounts of gastrin. This causes a variety of symptoms, collectively known as Zollinger-Ellison syndrome, principally due to ulcers that the acid causes.
These tumours arise in the so called 'gastrinoma triangle', an anatomical area illustrated here.
Gastrinoma triangle - click to enlarge
This is bound by the junction between the cystic duct and the common bile duct, the junction between the second and third parts of the duodenum and the junction between the head and neck of pancreas. Approximately 60% of tumours are in the pancreatic region of this area.
Roughly 60% of tumours are malignant, and even those characterised as benign can metastasise. However, unlike other tumours, the fact that the tumour may have begun to spread does not indicate that it is a more aggressive fast growing tumour that affects life expectancy.
Most are small (< 1cm) and therefore difficult to locate.