Duodenal gastrinoma: the solution to the pancreatic paradox.

There has been a recent focus of attention on the duodenum as a major source of gastrinomas. The question has often arisen as to why the pancreas should give rise to gastrinomas because, in the adult, it contains no gastrin-producing (G) cells. However, the numerous G cells of the duodenum may proliferate and function as a "carcinoid" lesion, producing a relatively indolent tumor, much like a papillary carcinoma of the thyroid. On the contrary, islet cells of the pancreas, which do not produce gastrin, may behave much like a neuroendocrine carcinoma and may be defined as a "pancreatic gastrinoma" because they produce an ectopic hormone (gastrin). These lesions are capable of behaving much more aggressively, as do many other ectopic hormone-producing neoplasms. The recognition of the difference between these two types of gastrinoma is of considerable clinical and biological significance.