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Basics of Brain Tumors

A brain tumor is a collection of cells that lose the ability to control their own growth. As they continue to grow in an uncontrolled way, they form a mass of cells that becomes a tumor. Brain tumors form in one of two ways:

  • A primary brain tumor starts with an abnormal brain cell and grows in the brain.

  • A metastatic tumor starts with an abnormal cell from another organ that makes its way into the brain, stays there, and multiplies to form a tumor made of that kind of cell. 

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. Brain tumors may be treated with surgery, radiation, drugs, or a combination of these.

A primary brain tumor can be malignant or benign.

  • A malignant tumor is more dangerous because it can grow quickly and may spread to other parts of the brain or to the spinal cord.  Malignant tumors are also called brain cancer. Metastatic brain tumors are always malignant because 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 they don't spread. In some cases, a benign tumor can turn into a malignant tumor.

Symptoms of a brain tumor may include:

  • Headache

  • Dizziness

  • Weakness

  • Vomiting

  • Changes in speech, vision, hearing, or personality

Types of brain tumors

More than 100 types of brain tumors have been identified, all named by the type of brain cell or part of the brain where they begin to grow. Men get more brain tumors than women, and the average age at the time the tumor is diagnosed is 55.

Location of different types of tumors
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Primary brain tumors include:

  • Astrocytoma. This is the most common type of malignant brain tumor. Half of all primary brain tumors are astrocytomas. They get their name from the star-shaped brain cells that make up the tumor. They can grow anywhere in the brain.

  • Meningioma. This is the most common type of benign brain tumor. It makes up about 35 percent of all primary brain tumors. These tumors start in the lining that covers the brain. In rare cases, they can become malignant.

  • Oligodendroglioma. These brain tumors form in the lining that covers nerves called "myelin." They are usually malignant.

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

  • Medulloblastoma. This tumor type is malignant and forms in the part of the brain near the spinal cord. It is most common in children younger than 10 years old. It can spread to the spinal cord and cause spinal fluid to back up into the brain.

  • Ependymoma. This tumor, which can be seen in young children and young adults, can range from benign to malignant. An ependymoma forms in the lining around fluid-filled areas of the brain.

  • Brain stem glioma. This tumor usually occurs in children between ages 3 and 10. It can be benign or malignant and occurs in the base of the brain.

Metastatic brain tumors are more common than primary brain tumors. These tumors usually occur in more than one area of the brain and are most common in older adults. 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 (WHO). A tumor's grade is determined by looking at cells from the tumor under a microscope. Tumor grading is important because it helps doctors decide how to treat a tumor.

Grade I and II tumors are 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, they rarely come back, and a patient can usually expect long-term survival.

  • Grade II. These tumors are considered to be malignant, but they grow slowly. They are less likely to spread, but they may recur after treatment.

  • Grade III. These tumors are malignant 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 and 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 that are leading to longer survival and better quality of life. Treatment will depend on age, overall health, and tumor grade. Learn as much as you can about brain tumors and work closely with your medical team to find the best treatment. 

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