Illustrate malignant tumors that form either in the brain or in the nerves originating in the brain. Brain cancer does not frequently spread to outside of the central nervous system . The CNS is the part of the nervous system that includes the brain and spinal cord. Primary brain cancer makes up to 4 % of all new cancer cases in adults and is the second most common form of childhood cancer. Primary brain cancer is the leading cause of cancer deaths in children and is the third most common cause of cancer deaths in adults aged 13 – 24.