Definition of Zollinger-Ellison syndrome:

Zollinger-Ellison syndrome is a condition that occurs with abnormal production of the hormone gastrin. 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 bowel. These tumors produce the hormone gastrin and are called gastrinomas. High levels of gastrin cause too much production of 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 commonly spread to the liver and nearby lymph nodes.

A number of patients with gastrinomas have many 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.