A brain tumor is a mass of abnormal cells that grows in or around the brain. It develops when abnormal cells multiply for unknown reasons. The words “benign” and “malignant” are used to describe brain tumors. Benign brain tumors are usually slow-growing and not cancerous. Malignant brain tumors are cancerous and are also called brain cancer. They tend to be aggressive, growing rapidly and destroying nearby brain tissue. This can lead to paralysis, weakness, blindness, strokes and even death.