Primary malignant tumors are more common than benign primary tumors. They occur in people of all ages, but are most common in people ages 55 to 65 and children ages 3 to 12. In primary malignant tumors, the cells replicate at a rapid rate, commonly infiltrate the brain and thus makes treating them with surgery very difficult. Secondary brain tumors occur when cancer cells from other areas of the body spread to the brain. Secondary tumors are the most common type of brain tumor.
Brain tumors occur when a cell proliferates in an abnormal manner.
There exist certain genes in a cell that control the cells ability to replicate. Two genes are implicated in cells that become cancerous. A cell that has an overactive oncogene or a defective tumor suppressor gene can become cancerous. Currently, investigation to identify these genes is at the forefront of cancer research. Clearly defined inherited factors play a minor role.