Basics of Brain Tumors

A brain tumor is a collection of cells that grow out of control. As they continue to grow, they form a mass of cells that becomes a tumor. Brain tumors form in 1 of 2 ways:

  • Primary brain tumor. This starts with an abnormal brain cell and grows in the brain.

  • Metastatic (secondary) tumor. This starts as a cancer in another part of the body, such as the lungs or breast. It then spreads to the brain, where it forms a new tumor. 

Doctors don't know why some cells begin to form into tumor cells. It may have something to do with a person's genes, or his or her environment, or both.

The tumors can cause local damage by growing and pushing on key areas of the brain. They can also cause problems if they block the flow of fluid around the brain. This can lead to an increase in the pressure inside the skull. Some types of tumors can spread through the spinal fluid to distant areas of the brain or the spinal cord.  

A primary brain tumor can be cancer (malignant) or noncancer (benign):

  • A malignant tumor is more dangerous because it can grow quickly. It may grow into or spread to other parts of the brain or to the spinal cord. Malignant tumors are also sometimes called brain cancer. Metastatic brain tumors are always cancer. They have spread to the brain from other areas of cancer in the body.

  • A benign primary brain tumor is not cancer. Benign tumors can cause damage by growing and pressing on other parts of the brain. But these tumors don't spread. In some cases, a benign tumor can turn into a malignant tumor.

Symptoms of a brain tumor depend on the size and location of the tumor, as well as other factors. They may include:

  • Headache

  • Dizziness

  • Weakness or numbness in the arms, legs, or face

  • Vomiting

  • Changes in speech, vision, hearing, or personality

  • Seizures

  • Feeling drowsy

  • Problems with balance or walking

Types of brain tumors

Both the type of brain tumor and its location are important. For example, some benign brain tumors can be quite harmful. They can cause severe neurological problems if located in a key area of the brain. More than 100 types of brain tumors have been identified. They are often named by the type of brain cell or part of the brain where they begin to grow.

Location of different types of tumors
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Some of the more common types of primary brain tumors include:

  • Astrocytoma. This is the most common type of cancer brain tumor. Its name comes from the star-shaped brain cells that make up the tumor. These tumors can grow anywhere in the brain.

  • Meningioma. This is the most common type of noncancer brain tumor. It makes up about 1 out of 3 of all primary brain tumors. These tumors start in the lining that covers the brain. In rare cases, they can become cancer.

  • Oligodendroglioma. These brain tumors form in the cells that make the lining that covers nerves, called myelin. These tumors are usually cancer.

Astrocytomas are common in children, as they are in adults. But they are less likely to be cancer. These are other common primary brain tumors in children:

  • Medulloblastoma. This tumor type is cancer. It forms in the back part of the brain called the cerebellum, near the spinal cord. It can spread to the spinal cord and cause spinal fluid to back up into the brain (hydrocephalus).

  • Ependymoma. This tumor can be seen in young children and young adults. It can range from cancer to noncancer. An ependymoma forms in the lining around fluid-filled areas of the brain (the cerebral ventricles).

  • Brain stem glioma. This tumor can be cancer or noncancer. It occurs in the base of the brain.

Metastatic brain tumors are more common than primary brain tumors in adults. These tumors usually occur in more than 1 area of the brain. The most common cancers that spread to the brain are lung, breast, colon, kidney, and melanoma skin cancers.

Grading primary brain tumors

Most cancer centers that treat brain tumors use a grading system developed by the World Health Organization. A tumor's grade is determined by looking at cells from the tumor under a microscope. Tumor grading is important because it is one factor that helps doctors decide how to treat a tumor.

Grade I and II tumors are typically considered low grade. They look more normal under the microscope, are less likely to spread, and are easier to treat. Grade III and IV tumors are considered high grade. They grow more quickly and are harder to treat. Over time, some low-grade tumors become high-grade tumors.

Here is more specific information on tumor grades:

  • Grade I. These tumors are considered to be benign and slow growing. They may be treated with surgery and they rarely come back. You can often expect long-term survival.

  • Grade II. These tumors are considered to be cancer, but they grow slowly. They are less likely to spread. But they may come back after treatment.

  • Grade III. These tumors are cancer and tend to spread to other parts of the brain. They may come back as grade IV after treatment.

  • Grade IV. These are the most malignant tumors. They grow and spread most rapidly. They are least likely to be cured.

If you or a loved one has been diagnosed with a brain tumor, keep in mind that many new treatments are available. These are leading to longer survival and better quality of life. Treatment will depend on a person's age, overall health, and the tumor type, grade, location, and other factors. Learn as much as you can about brain tumors and work closely with your medical team to find the best treatment.