A brain tumor is a growth of abnormal cells or normal cells in an inappropriate place in the brain. The growth may be malignant (cancerous) or benign (noncancerous). The brain and the spinal cord are the main components of the central nervous system (CNS). The brain is composed of a number of different types of cells and tissues. Any of these can form tumors. Some of the tumors are a combination of cell types.

According to the National Cancer Institute (NCI), brain tumors account for 85 to 90 percent of all primary CNS tumors. A primary CNS tumor develops from cancer cells within the central nervous system rather than cancer cells that have spread (metastasized) to the CNS.

Tumors can occur in all areas of the brain. Each part of the brain controls certain functions, and tumors in these different areas disrupt the function of that area. The main areas of the brain are:

• Cerebral hemispheres. Control speech, language, thought, reasoning and emotion. The left and right hemispheres also are responsible for muscle movements and interpreting sensory information.
  
  
• Basal ganglia. Help control muscle movements.
  
  
• Cerebellum. Controls coordination of movement and balance. This part of the brain helps coordinate large motor skills such as walking as well as fine motor movements necessary for speech and use of the fingers.
  
  
• Brain stem. Contains bundles of nerves that transmit signals for control of muscles or feeling. This area also controls basic functions such as breathing and the beating of the heart.

Brain tumors can either develop within the brain (primary) or develop from cancer cells that spread to the brain (metastatic or secondary).  Primary tumors may be noncancerous or cancerous. Metastatic brain tumors, however, can only be malignant. According to the NCI, metastatic brain tumors are much more common than primary brain tumors. It is estimated that metastatic brain tumors outnumber primary brain tumors by 10 to 1.

Despite their harmless-sounding name, benign tumors can create problems, such as compressing the spinal cord, blood vessels or other important structures. Even though they are not cancerous, they may need to be treated with surgery or other methods.

According to the American Cancer Society (ACS), approximately 20,500 malignant tumors of the brain or spinal cord will be diagnosed in the United States in 2007. Nearly 13,000 deaths from CNS cancers are expected in 2007. These types of cancer account for approximately 1.3 percent of all the cancers and 2.2 percent of all cancer-related deaths. These statistics include adults and children with CNS tumors.

The survival time for individuals with malignant brain tumors varies with the type of cancer. For example, according the ACS, the survival time for patients with low–grade (see Types and differences) is approximately six to eight years. The average survival rate for patients with glioblastomas is approximately 12 months.

In addition, the five-year survival for all people with brain cancer varies with age. The five-year survival rate refers to the percentage of patients who live at least five years after their cancer is diagnosed. Five-year rates are used by healthcare professionals as a standard means of discussing prognosis. Many individuals live longer than the five years.

The five-year survival rate according to age for malignant brain tumors is as follows:

Many types of brain cancers can be successfully treated with one or more treatment methods. The five-year survival rates for more recently diagnosed patients may be improved because of advanced technology and more effective treatments.