The body is made up of many types of cells with each having its own special function. Most cells grow and then divide in an orderly way to form new cells as they are needed to keep the body functioning properly. When normal cells lose the ability to control their growth, they divide too often and without any order. The extra cells form a mass of tissue called a tumor, which can be benign or malignant.

• Benign brain tumors do not contain cancer cells. They consist of slow growing cells, have distinct borders, and rarely spread.
• Malignant brain tumors contain cancer cells. They are likely to grow rapidly and invade surrounding normal brain tissue.

There are two basic types of malignant (or cancerous) brain tumors: primary brain tumors and metastatic brain tumors. Primary brain tumors are tumors that originate in the brain. Metastatic brain tumors are caused by cancer that begins in another part of the body and then spreads to the brain. Each year approximately 17,000 people in the United States are diagnosed with primary brain tumors and over 150,000 people are diagnosed with metastatic brain tumors.

Primary brain tumors are classified by the type of tissue from which they originate. The most common brain tumors are gliomas, which begin in the glial (supportive) tissue.

Treatment for a malignant brain tumor depends on a number of factors, including:

• type, location, and size of the tumor
• patient's age and general health

A common problem with malignant brain tumor therapy is recurrence. Cancerous tumors often come back within a short period of time after treatment. And when they do, they usually grow in or near the same place as the original tumor. Over 80% of recurrences are within 2 cm of the previous tumor location.