There are two main types of brain tumors: those that start in the brain (primary) and those that spread from cancer somewhere else in the body (metastasis). Primary brain tumors, such as a glioma, happen less often, and when they do, they are mostly malignant (cancerous). A malignant tumor is a mass or clump of cancer cells that keeps growing; it doesn't do anything except feed off the body so it can grow.
Gliomas (glee-OH-muhs) make up the largest group of primary brain tumors. There are several kinds of gliomas: astrocytomas, which grow anywhere in the brain or spinal cord; brain stem gliomas, which arise in the lowest part of the brain; ependymomas, which develop inside the brain, in the lining of the ventricles, and oligodendrogliomas, which usually grow in the cerebrum (very rare, representing just 3% of all primary brain tumors). An advanced astrocytoma is called glioblastoma; these represent 23% of all primary brain tumors.
According to the American Brain Tumor Association, primary brain tumors occur at a rate of 12.8 per 100,000 people. Although people of any age can develop a brain tumor, the problem seems to be most common in children ages 3 to 12 and in adults ages 40 to 70. In the United States, approximately 2,200 children younger than age 20 are diagnosed annually with brain tumors. In the past, physicians did not think about brain tumors in elderly people. Due to increased awareness and better brain scanning techniques, people 85 years old and older are now being diagnosed and treated.
Difficult to treat
Tumors growing in the brain are difficult to treat. One type of treatment is external beam radiation, in which radiation passes through the brain to the tumor. Unfortunately, this exposes healthy brain tissue to potentially damaging radiation. Another treatment is surgical removal of the tumor, if possible, followed by chemotherapy. All of these treatments are difficult to go through, and pose risks to the patient. Unfortunately, many gliomas grow back even after treatment.
There are several reasons why it is hard to get rid of these types of brain tumors. Some drugs can't get into the brain because of a special filtering mechanism in the body (called the blood-brain barrier). Some tumors spread into (infiltrate) the tissues around them with tiny projections. Many tumors have more than one kind of cell in them, so chemotherapy directed at one kind of cell in the tumor will not kill the other cells.