In most cases the cause of a brain tumor is unknown however several factors increase a persons risk of developing a brain tumor having risk factors does not mean you will get a brain tumor and many people with brain tumors have no known risk factors even if you have risk factors and develop a brain tumor doctors can rarely determine . The only known environmental risk factor for brain tumors is exposure to radiation usually from radiation therapy for other cancers such as leukemia the acs also say that most people with brain. Risk factors for brain tumors include family history only about 5 to 10 percent of all cancers are genetically inherited or hereditary its rare for a brain tumor to be genetically inherited . Doctors dont know all of the risk factors associated with brain tumors but here are some exposure to high doses of radiation this could include radiation used near the head to treat a cancer