A risk factor is something that raises a person's chances of getting sick. For example, cigarette smoking is a risk factor for lung cancer, while obesity is a risk factor for heart disease. The more factors you have, the higher your chance of getting sick. Brain tumors are the most common type of cancer in children. They're also the most frequent cause of death from cancer in children under 15 years old. Around 85% of brain tumors are malignant (cancerous). The rest are benign (not cancerous). The main types of brain tumor are as follows: • Astrocytomas are cancers of support cells. They grow slowly and can be treated with surgery alone. The average age at which people develop astrocytomas is about 40 years old. Men are usually affected more than women. The most common site for an astrocytoma to appear is inside the skull, but it can also appear elsewhere in the brain. • Ependymomas are cancers of the lining of the ventricles (the space within the brain where cerebrospinal fluid is kept). Children tend to develop ependymomas near their spine or head. The average age at which people develop them is around 10 years old.