image source: www.science.nationalgeographic.com
There are two main types of brain tumors: those that start in the brain (primary) and those that spread from cancer somewhere else in the body (metastasis). Primary brain tumors happen less often, and when they do, they are mostly malignant (cancerous). A malignant tumor is a mass or clump of cancer cells that keeps growing; it doesn’t do anything except feed off the body so it can grow.
The largest group of primary brain tumors is gliomas (glee-OH-muhs). There are several kinds of gliomas: astrocytomas, which grow anywhere in the brain or spinal cord; brain stem gliomas, which arise in the lowest part of the brain; ependymomas, which develop inside the brain, in the lining of the ventricles, and oligodendrogliomas, which usually grow in the cerebrum (very rare, representing just 3% of all primary brain tumors). An advanced astrocytoma is called glioblastoma; these represent 23% of all primary brain tumors.