The incidence of pituitary tumors is increased in multiple endocrine adenomatosis or neoplasia (MEA or MEN) (especially type I: autosomal dominant inheritance with high penetrance, also involves pancreatic islet cell tumors (which may produce gastrin and hence Zollinger-Ellison syndrome) and parathyroids (hyperparathyroidism), and in which the pituitary tumors are usually nonsecretory).