A brain tumor occurs when there is a genetic alteration in the normal cells in the brain. The alteration causes the cells to undergo a series of changes that result in a growing mass of abnormal cells. Primary brain tumors involve a growth that starts in the brain, rather than spreading to the brain from another part of the body.
Brain tumors may be low grade (less aggressive) or high grade (very aggressive). The cause of primary brain tumors is unknown, although some tumors have germ line mutations and tend to be hereditary. The majority result from somatic mutations and are not hereditary.
Central nervous system tumors (tumors of the brain and spine) are the most common solid tumor in children. There are approximately 4,500 new brain tumors each year, and they are the most common cause of cancer deaths.
Low Grade Gliomas
Low-grade gliomas are brain tumors that originate from glial cells, which support and nourish neurons in the brain. Glial tumors, or gliomas are divided into four grades, depending on their cells' appearance under a microscope. Grade 1 and 2 gliomas are considered low-grade and account for about two-thirds of all pediatric tumors.
In addition to their grade, low-grade gliomas are also classified based on their location and by the kind of glial cell – astrocytes, oligodendrocytes or ependymocytes – from which they arise.
High Grade Gliomas
Glioblastoma Multiformes (GBMs) are high-grade gliomas that arise from the brain’s supportive tissue, known as glial cells. These are aggressive tumors that rapidly infiltrate adjacent healthy brain tissue and, as a result, are difficult to treat.
The majority of GBMs, roughly 65%, occur in the cerebral hemispheres, which control higher functions like speech, movement, thought and sensation. They can also develop in the part of the brain that identifies sensations such as temperature, pain and touch and the region of the brain that controls balance and motor function.
These tumors are usually diagnosed between the ages of 5 and 9, and occur in boys and girls equally. GBMs occur with increased frequency in children with certain genetic syndromes, including neurofibromatosis 1, Li-Fraumeni syndrome, hereditary nonpolyposis colon cancer and tuberous sclerosis. Most GBMs, however, have no known cause.