 [ Symptoms ] what causes brain tumors [ Disease ] no one knows what causes brain tumors there are only a few known risk factors that have been established by research people who receive radiation therapy to the head as a child have a higher risk of a brain tumor over the next 20 to 30 years people who have certain rare genetic conditions such as neurofibromatosis    a disorder of the nervous system    or li fraumeni syndrome    a condition that predisposes someone to developing cancer    are also at higher risk but radiation therapy or rare genetic disorders are only a factor in a small number of the approximately 35 000 new primary brain tumors diagnosed each year finally age is a factor the rate of developing brain cancer is four times the rate each year in people over the age of 65 than in people younger than 65