Causes
Zollinger-Ellison syndrome is caused by tumors. These growths are most often found in the head of the pancreas and the upper small intestine. The tumors are called gastrinomas. High levels of gastrin cause production of too much stomach acid.
Gastrinomas occur as single tumors or several tumors. One-half to two-thirds of single gastrinomas are cancerous (malignant) tumors. These tumors often spread to the liver and nearby lymph nodes.
Many people with gastrinomas have several tumors as part of a condition called multiple endocrine neoplasia type I (MEN I). Tumors may develop in the pituitary gland (brain) and parathyroid gland (neck) as well as in the pancreas.