Primary Brain Tumors - Patient Information

Information for Physicians
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Definitions

Brain tumors are tumors that grow in the brain. A tumor is an abnormal growth caused by cells reproducing themselves in an uncontrolled manner.

When doctors describe tumors in parts of the body other than the brain, they use the words benign (meaning harmless) or malignant (meaning cancerous). These meanings change, however, when referring to tumors in the brain.

Benign brain tumors
A benign brain tumor consists of benign (harmless) cells and has distinct boundaries. Surgery alone may cure this type of tumor.

Malignant brain tumors
A malignant brain tumor is life-threatening. It may be malignant because it consists of cancer cells, or it may be called malignant because of its location. In other words, a brain tumor composed of benign cells--but located in a vital area--is still considered malignant.

A malignant brain tumor made up of cancerous cells may spread or seed (metastasize) to other locations in the brain or spinal cord. It can invade and destroy healthy tissue so it cannot function properly. Malignant tumors grow the way a plant does, with "roots" invading various tissues. Or, they can shed cells that travel to distant parts of the brain. Some cancerous tumors, however, remain localized.

Malignant brain tumors seldom metastasize outside the brain and spinal cord. [Central Nervous System (CNS)]

The bones of the skull hide brain tumors. The doctor can not feel or see them during a routine examination. Scans produce pictures that suggest a particular type of tumor. Only a sample of tumor examined under a microscope can provide an exact diagnosis . If this type of examination is not possible, an educated assumption is made based on available test results.

Often, the damage done by brain tumors is due to their size. Because the skull is bone, it cannot expand to make room for even a small mass growing within it. As a result, the tumor presses on and displaces normal brain tissue. This pressure may damage or destroy delicate brain tissue. Many of the symptoms of a brain tumor are caused by this pressure. Sometimes, a tumor may cause blockage of fluid that flows around and through the brain. This blockage can also create increased pressure. Some brain tumors also cause swelling due to accumulation of fluid (edema). Size, pressure, and swelling all create this "mass effect."

Category
Tumors that start in the brain are primary brain tumors.

Metastatic brain tumors are tumors formed by cancer cells that start elsewhere in the body and spread to the brain.
Naming Tumors

Tumor names depend on where the tumor originated, its pattern of growth, and whether it is cancerous or not. The following are some general names of tumors:

Adenoma
A usually benign tumor arising from a gland; for example, pituitary adenoma.

Blastoma
A malignant tumor whose cells have undeveloped(embryonic) characteristics; for example, medulloblastoma or glioblastoma multiforme.

Carcinoma
A malignant tumor that arises from skin or the lining of the digestive, respiratory, and urogenital systems; for example, lung cancer (small cell carcinoma) or colon cancer (adenocarcinoma).

Sarcoma
A malignant tumor that arises from connective tissue, blood vessels, or the lymph system; for example, osteosarcoma.

Glioma
The general name for a tumor that arises from the supportive tissue of the brain; for example, astrocytoma or oligodendroglioma. It may be benign or malignant.

Some tumors may undergo further change (mutation). A benign growth may become malignant. In some tumors, a lower-grade tumor may recur as a higher-grade tumor.

Grading Tumors

Tumor grade indicates the degree of malignancy. Grade is based on the tumor's tendency to spread (infiltrate), its growth rate, and its similarity to normal cells.

Tumors with distinct borders (circumscribed), considered grade I, are sometimes referred to as benign or mildly malignant. Those tumors either do not grow or grow slowly.

Infiltrating tumors are those that tend to grow into surrounding tissue. Of the infiltrating tumors, the terms low-grade, mid-grade, and high-grade are frequently used. However, the exact system used to grade tumors varies with each specific family of tumors.

Tumors often contain several grades of cells. The highest or most malignant grade of cell found during microscopic examination determines the grade, even if most of the tumor is a lower grade.

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