A pituitary tumor is an abnormal grouping of cells on the pituitary gland, a small but important gland at the base of the brain. Most pituitary tumors are non-cancerous (benign), and are most often seen in older adults. Some pituitary tumors can affect hormones in the body, causing different conditions and symptoms associated with an abundance or not enough of the hormones that regulate the body’s systems. Tumor pressure can cause headaches, vision loss, and weight loss/gain.