DrJHO's site has a good write up on Tumors
I am keeping this as a reminder of Acromegaly- a functioning tumor
"Benign pituitary adenomas can be divided into nonfunctioning tumors and functioning tumors depending on the capability of tumor cells to produce hormones. Nonfunctioning pituitary adenomas do not produce active hormones by themselves. Nonfunctioning tumors mechanically compress surrounding structures such as normal pituitary gland and optic system. Functioning pituitary adenomas produce a hormone(s) in excess. Excess amount of hormone produced by tumor cells cause symptoms dependent on the type of hormone. Functioning pituitary adenomas include prolactinomas (PRL overproduction), adenomas that cause Cushing's disease (ACTH overproduction), adenomas that cause gigantism or acromegaly (GH overproduction), and TSH-producing tumors."