Brain Tumor Facts

A brain tumor is defined as any abnormal or uncontrolled growth of cells in the brain. Tumors can be either benign, (non-cancerous), or malignant (they may be cancerous).  It is important to recognize that even a benign brain tumor can be dangerous because as a tumor in the brain grows, it presses upon normal brain tissues, which can cause inflammation and brain swelling. It is therefore very important that both benign and malignant brain tumors be treated as early as possible. 

A primary brain tumor results when a tumor originates in the brain itself. When cancer metastasizes - or spreads from other areas, such as the lungs or the breasts - to the brain, a secondary (or metastatic) brain tumor results. Brain tumors are less common than other cancers, but they are considered to be dangerous due to their location and sometimes aggressive nature.

Classification of Brain Tumors
Primary brain tumors are classified by the type of tissue in which they begin. The most common primary brain tumors are gliomas, which begin in the glial (supportive) tissue. There are several types of gliomas:

  • Astrocytomas arise from small, star-shaped cells called astrocytes. They may grow anywhere in the brain or spinal cord. In adults, astrocytomas most often arise in the cerebrum. In children, they occur in the brain stem, the cerebrum, and the cerebellum. A grade III astrocytoma is sometimes called anaplastic astrocytoma. A grade IV astrocytoma is usually called glioblastoma multiforme.
  • Brain stem gliomas occur in the lowest, stemlike part of the brain. Tumors in this area generally cannot be removed. Most brain stem gliomas are high-grade astrocytomas.
  • Ependymomas usually develop in the lining of the ventricles. They may also occur in the spinal cord. Although these tumors can develop at any age, they are most common in childhood and adolescence.
  • Oligodendrogliomas arise in the cells that produce myelin, the fatty covering that protects nerves. These tumors usually arise in the cerebrum. They grow slowly and usually do not spread into surrounding brain tissue. Oligodendrogliomas are rare and occur most often in middle-aged adults, but they have been found in people of all ages.

There are other types of primary brain tumors that do not begin in glial tissue. Some of the most common are:

  • Medulloblastomas. Recent research suggests that these tumors develop from primitive (developing) nerve cells that normally do not remain in the body after birth. For this reason, medulloblastomas are sometimes called primitive neuroectodermal tumors (PNET). Most medulloblastomas arise in the cerebellum, but they may occur in other areas as well. These tumors occur most often in children and are more common in boys than in girls.
  • Meningiomas grow from the meninges and are usually benign. Because these tumors grow very slowly, the brain may be able to adjust to their presence. Meningiomas often grow quite large before they cause symptoms. They occur most often in women between 30 and 50 years of age.
  • Schwannomas are benign tumors that begin in Schwann cells, which produce the myelin that protects the acoustic nerve - the nerve of hearing.
  • Acoustic neuromas are a type of schwannoma. They occur mainly in adults and affect women twice as often as men.
  • Craniopharyngiomas develop in the region of the pituitary gland near the hypothalamus. They are usually benign; however, they are sometimes considered malignant because they can press on or damage the hypothalamus and affect vital functions. These tumors occur most often in children and adolescents.
  • Germ cell tumors arise from primitive (developing) sex cells, or germ cells. The most frequent type of germ cell tumor in the brain is the germinoma.
  • Pineal region tumors occur in or around the pineal gland, a tiny organ near the center of the brain. The tumor can be slow growing (pineocytoma) or fast growing (pineoblastoma). The pineal region is very difficult to reach, and these tumors often cannot be removed.

Benign Brain Tumors
Benign brain tumors do not contain cancer cells. They usually can be removed, and are not likely to recur. Benign brain tumors have clear borders. These tumors do not invade nearby tissue.  However, they can press on sensitive areas of the brain.

Malignant Brain Tumors
Malignant brain tumors contain cancer cells and interfere with vital functions. Malignant brain tumors are likely to grow rapidly and crowd or invade the tissue around them. Like a plant, these tumors may put out "roots" that grow into healthy brain tissue. If a malignant tumor remains compact and does not have roots, it is said to be encapsulated. When an otherwise benign tumor is located in a vital area of the brain and interferes with vital functions, it may be considered malignant (even though it contains no cancer cells).

Some brain tumors are referred to by grade - from low grade (grade I) to high grade (grade IV). The grade of a tumor refers to the way the cells look under a microscope. Cells from higher grade tumors are more abnormal looking and generally grow faster than cells from lower grade tumors; higher grade tumors are more malignant than lower grade tumors.

Tumor-Specific Statistics
Metastatic brain tumors are the most common brain tumor, with an annual incidence more than four times greater than that of primary brain tumors. The cancers that most commonly metastasize to the brain are breast and lung cancers.

  • Meningiomas represent 24% of all primary brain tumors, making meningiomas the most common primary brain tumor.
  • Glioblastomas represent 23% of all primary brain tumors.
  • Astrocytoma and pituitary tumors each represent 8% of all primary brain tumors.
  • Nerve sheath tumors (such as acoustic neuromas, vestibular schwannomas, neurilemmomas) represent 6% of all primary brain tumors.
  • Anaplastic astrocytomas and lymphomas each represent 4% of all primary brain tumors.
  • Oligodendrogliomas represent 3% of all primary brain tumors.

Led by Farnaz Arabshahi, RN, the Brain Tumor support group provides a comfortable setting for patients, families, friends and caregivers to share their experiences, learn about current therapies, hear interesting speakers who provide information about all aspects of diagnosis and treatments. 

Additional information

American Brain Tumor Association
The Brain Tumor Society
National Brain Tumor Foundation