is a slow-growing, benign tumor of the pituitary gland that is a functioning tumor (secreting hormones) or a nonfunctioning tumor (not secreting hormones).
Typically benign tumors, adenomas often press on the pituitary gland, causing loss of function of one or more hormones. Many pituitary adenomas are called âfunctioning tumorsâ because they actually make hormones and may cause an increase in hormone levels instead of a decrease.