A tumor is abnormal tissue that grows by uncontrolled cell division. Normal cells grow in a controlled manner as new cells replace old or damaged ones. For reasons not fully understood, tumor cells reproduce uncontrollably. Brain tumors are named after the cell type from which they grow. They may be primary (starting in the brain) or secondary (spreading to the brain from another area). Treatment options vary depending on the tumor type, size and location; whether the tumor has spread; and the age and medical health of the person.
Brain Tumors: An Introduction.pdf