Pituitary adenomas are tumors that occur in the pituitary gland. Pituitary tumors are generally divided into three kinds dependant upon their biological functioning: benign adenoma, invasive adenoma or carcinomas, with carcinomas accounting for 0.1% to 0.2%, appoximately 35% being invasive adenomas and most being benign adenomas. Pituitary adenomas represent from 10% to 25% of all brain tumors and is thought to happen in about 17% to 25% of most people.