There are many types of brain and spinal cord tumors. The tumors are formed by the abnormal growth of cells and may begin in different parts of the brain or spinal cord. Together, the brain and spinal cord make up the central nervous system (CNS). The tumors may be either benign (not cancer) or malignant (cancer): Benign brain and spinal cord tumors grow and press on nearby areas of the brain. They rarely spread into other tissues and may recur (come back). Malignant brain and spinal cord tumors are likely to grow quickly and spread into other brain tissue. (source : National Cancer Institute).