Definition of Zollinger-Ellison syndrome:

Zollinger-Ellison syndrome is a condition in which there is increased production of the hormone gastrin. Usually, a small tumor (gastrinoma) in the pancreas or small intestine produces the high levels of gastrin in the blood.

Causes, incidence, and risk factors:

Zollinger-Ellison syndrome is caused by tumors, usually found in the head of the pancreas and the upper small intestine. These tumors produce the hormone gastrin and are called gastrinomas. High levels of gastrin cause production of too much stomach acid.

Gastrinomas occur as single tumors or as small, multiple tumors. About one-half to two-thirds of single gastrinomas are cancerous (malignant) tumors that often spread to the liver and nearby lymph nodes.

Many patients with gastrinomas have several tumors as part of a condition called multiple endocrine neoplasia type I (MEN I). MEN I patients often have tumors of the pituitary gland (brain) and parathyroid gland (neck), as well as tumors of the pancreas.