Overview

The brain and spinal column make up the central nervous system (CNS), where all vital functions, including thought, speech, and strength of the body are controlled. When a tumor arises in the CNS, it is especially problematic because of the potential effect on a person's thought processes and movements.

A brain tumor begins when cells in the brain begin to grow uncontrollably and eventually form a mass. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread). Malignant brain tumors are further classified using a grade: low, intermediate, or high. More information can be found in Staging/Grading.

This section describes primary brain tumors, which are tumors that begin in the brain. Secondary brain tumors (also called brain metastases) are much more common than primary tumors. A secondary brain tumor is a cancerous tumor that started in another part of the body (such as the breast, lung, or colon) and then spread to the brain. For cancer that started elsewhere in the body and spread to the brain, learn more information by reading the Cancer Type section where the cancer began.

Anatomy of the brain

The brain is made up of four main parts: the cerebrum, the cerebellum, the brain stem, and the meninges.

The cerebrum. This is the largest part of the brain, contains two cerebral hemispheres and is divided into four lobes where specific functions occur:

• The frontal lobe, which controls reasoning, emotions, problem-solving, expressive speech and movement
  
  
• The parietal lobe, which controls the sensations of touch, pressure, pain, temperature, and parts of speech, visual-spatial orientation, and calculation
  
  
• The temporal lobe, which controls memory, the special senses, such as hearing, and the ability to understand spoken or written words
  
  
• The occipital lobe, which controls vision

The cerebellum. This is located beneath the cerebrum. The cerebellum is located at the back part of the brain below the cerebrum. It is responsible for coordination and balance.

The brain stem. This is the portion of the brain that connects to the spinal cord, controls involuntary functions essential for life, such as the beating of the heart and breathing. In addition, messages for all the functions controlled by the cerebrum and cerebellum travel through the brain stem to the connections in the body.

The meninges. These are the membranes that surround and protect the brain and spinal cord. There are three meningeal layers, called the dura mater, arachnoid, and pia mater. The cerebrospinal fluid (CSF) is produced near the center of the brain, in the lateral ventricles, and circulates around the brain and spinal cord between the arachnoid and pia layers.

Types of brain tumors

There are more than 100 types of primary brain tumors. For a complete listing of their names and incidence, please refer to the Central Brain Tumor Registry of the United States. This section covers brain tumors diagnosed in adults. (For brain tumors in children, read more about childhood brain tumors in another section of Cancer.Net.) For practical purposes, this section’s coverage is divided into gliomas and non-glioma types of tumors in adults:

Gliomas

As a group, a glioma is considered the most common type of brain tumor. A glioma is a tumor that grows from a glial cell, which is a supportive cell in the brain. There are two types of supportive cells: astrocytes and oligodendrocytes. Most gliomas are called either astrocytoma or oligodendroglioma, or a mixture of both. A glioma is given a grade (a measure of how much the tumor appears like normal brain tissue) from I to IV (one to four) based on the degree of aggressiveness. A grade I glioma is a benign tumor, while grades II through IV are tumors with an increasing degree of aggressiveness and are therefore considered increasingly cancerous in potential.

Types of gliomas include:

Astrocytoma. Astrocytoma is the most common type of glioma and begins in cells called astrocytes in the cerebrum or cerebellum. There are four grades of astrocytoma.

• Grade I or pilocytic astrocytoma is a slow-growing tumor that is most often benign and rarely spreads into nearby tissue. It accounts for about 2% of all brain tumors.
  
  
• Grade II or low-grade diffuse astrocytoma is a slow-growing tumor that can often spread into nearby tissue and can become a higher grade. It accounts for about 11% of all brain tumors.
  
  
• Grade III or anaplastic astrocytoma is a malignant tumor that can quickly grow and spread to nearby tissues. It accounts for about 3% of all brain tumors.
  
  
• Grade IV or glioblastoma multiforme is a very aggressive form of astrocytoma that accounts for about 20% of all brain tumors.

For more information on astrocytoma in children, read the guide to Astrocytoma, Childhood Cancer.

Oligodendroglioma. Oligodendroglioma is a tumor that develops from cells called oligodendrocytes. These cells are responsible for producing the myelin (a substance rich in protein and lipids [fatty substances]) that surrounds nerves. Oligodendrogliomas make up about 4% of primary brain tumors and are subclassified as either oligodendrogliomas (considered low grade) or anaplastic oligodendroglioma.

Mixed gliomas. A mixed tumor is composed of more than one of the glial cell types and makes up about 1% of primary brain tumors.

Ependymomas. Ependymomas begin in the ependyma (the cells that line the passageways in the brain where CSF is made and stored) and make up about 2% of primary brain tumors. For pediatric information, read the guide to Ependymoma, Childhood Cancer.

Brain stem glioma. A brain stem glioma begins in the glial cells in the brain stem. Read guide to Brain Stem Glioma, Childhood Cancer for pediatric information.

Non-glioma tumors

As explained above, this section covers non-glioma tumors, which are tumors that arise from cells in the brain that are not glial (supportive) tissue. Types of non-glioma tumors include:

Meningioma. Meningioma is the most common primary brain tumor, making up about 30% of all primary brain tumors. It begins in the meninges and is most often benign. Meningioma can cause significant symptoms if it grows and presses on the brain or spinal cord or invades into the brain tissue. Read the guide to Meningioma for more information.

Pineal gland and pituitary gland tumors. The pineal gland and pituitary gland are the locations of about 7% of all brain tumors.

Primary CNS lymphoma. This is a form of lymphoma (cancer that begins in the lymphatic system) that starts in the brain and can spread to the spinal fluid and eyes. It makes up about 3% of all brain tumors.

Medulloblastoma. Medulloblastoma begins in granular cells in the cerebellum. It is most common in children and is most often malignant, often spreading throughout the CNS. Medulloblastomas make up about 2% of all brain tumors. Similar tumors can arise in other parts of the brain, frequently in the pineal gland region, and are called Primitive Neuro Ectodermal Tumors (PNET) For pediatric information, refer to guide to Medulloblastoma, Childhood Cancer.

Craniopharyngioma. Craniopharyngioma is a benign tumor that begins near the pituitary gland located near the base of the brain. These tumors are rare, making up less than 1% of all brain tumors. For pediatric information, read the guide to Craniopharyngioma, Childhood Cancer.

Acoustic schwannoma. Acoustic schwannoma (also called acoustic neuroma or vestibular schwannomas) is a rare tumor that begins in the vestibular nerve (a nerve in the inner ear that helps control balance) and is normally benign.

About 6% of all brain tumors cannot be assigned an exact type.

Statistics

It is estimated that about 52,000 people will be diagnosed with a primary brain tumor (benign or malignant) each year.

In 2009, an estimated 22,070 adults (12,010 men and 10,060 women) in the United States will be diagnosed with primary malignant tumors of the brain and spinal cord. It is estimated that 12,920 deaths (7,330 men and 5,590 women) from this disease will occur this year. Brain tumors are the tenth most common cause of cancer death in women.

Metastatic or secondary tumors of the brain will occur in 20% to 40% of patients with cancer. The most common primary cancers that spread to the brain are lung, breast, unknown primary, melanoma, and colon cancers.

Survival statistics should be interpreted with caution. Estimates are based on data from thousands of cases of brain tumors in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with a brain tumor. Because the survival statistics are measured in five-year (or sometimes one-year) intervals, they may not represent advances made in the treatment or diagnosis of this cancer.

Statistics adapted from the American Cancer Society’s publication, Cancer Facts & Figures 2009, the National Cancer Institute, and the Central Brain Tumor Registry.

Find out more about basic cancer terms used in this section.

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Last Updated: July 17, 2009