Types and Grades of Brain Tumors
Staging Brain Cancer
Unlike other cancers, brain cancer is assigned a “grade” rather than a stage, based on how the cells look under the microscope. The most commonly used brain cancer grading system, developed by the World Health Organization (WHO), is as follows:
- Grade I: Tumors are typically slow-growing and localized (not growing into nearby tissue). Grade I tumors can often be cured with surgery.
- Grade II: Tumors are slow-growing but invasive to nearby brain tissue. Grade II tumors have a higher chance of recurrence (come back) and can change into a faster-growing tumor over time.
- Grade III: Tumors are visibly abnormal under the microscope and can grow into nearby brain tissue. Often, other treatments (in addition to surgery) are needed.
- Grade IV: Tumors are the fastest growing and typically require aggressive treatment.
Types of Brain Tumors
There are more than 130 different types of brain tumors, many with their own multitude of subtypes.
Common Types of Brain and Spinal Tumors
There are two more common types of brain and spinal tumors that can occur in adults.
- Meningiomas, which originate in the meninges, the layers of tissue that surround the outer part of the brain and spinal cord
- Gliomas, which originate in the glial (supportive) tissue
Less Common Types of Brain and Spinal Tumors
Less common tumors, which either account for a very low percentage of brain and spinal tumors or are more common among children than adults, may include:
- Astrocytomas are tumors that start in glial cells called astrocytes. About two out of ten brain tumors are astrocytomas.
- Schwannomas, which develop from Schwann cells - cells that surround and insulate cranial nerves - account for about 8% of all primary brain tumors.
- Oligodendrogliomas, which start in brain glial cells called oligodendrocytes. About 4% of primary brain tumors are oligodendrogliomas.
- Ependymomas, which are tumors that start in the ependymal cells that line the ventricles. They account for 2-3% of primary brain tumors.
- Medulloblastomas, which are tumors that develop from neuroectodermal cells (early forms of nerve cells) in the cerebellum. Medulloblastomas occur much more often in children than in adults.
- Gangliogliomas, which are slow-growing tumors that contain both neurons and glial cells. These tumors are very uncommon in adults.
- Craniopharyngiomas, which start above the pituitary gland but below the brain. Craniopharyngiomas are more common in children, but they are sometimes seen in adults.
- Chordomas, which are rare tumors that start in the bone at the base of the skull or at the lower end of the spine. Although they don’t start in the central nervous system, they can injure the nearby brain or spinal cord by pressing on it.
- Non-Hodgkin lymphomas, which starts in the white blood cells called lymphocytes (a primary cell type of the immune system). These lymphomas are more common in people with immune system problems, such as those infected with HIV, the virus that causes AIDS. However, in recent years, these lymphomas have become less common because of new treatments for AIDS.
Pituitary tumors, which start in the pituitary gland. In most cases, pituitary tumors are benign, slow-growing masses that represent about 10% of primary brain tumors.