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 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 deep 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.
Twists on Traditional Treatments
New ways of treating brain tumors are being investigated, including modifying existing treatments as well as developing new ways to give the treatments.
To get chemotherapy drugs past the blood-brain barrier, for example, researchers are increasing the dosages and injecting the drugs directly into the blood vessels of the brain. A new method puts the chemotherapy right at the tumor site. After surgery, small biodegradable plastic wafers can be put in where the tumor was. These wafers release chemotherapy drugs right there.
Something similar can be done with radiation therapy. After a tumor is removed, a surgical balloon is put in the cavity left by the tumor. The balloon is filled with liquid radiation, and over the next week, it radiates the tissue around it to kill off any remaining cancer cells.
Researchers are looking at tumor treatment from many exciting angles. One of these approaches is antiangiogenesis. This means cutting off the blood supply to a tumor so that not only will it not grow, it will shrink and die. One study tried an antioangiogenic drug, Thalidomide, with patients who had very serious gliomas that hadn’t responded to radiation and/or chemotherapy. One year after starting the drug, 25% of the patients were still alive, although their tumors were still growing. The researchers suggested that perhaps Thalidomide could be tried in newly-diagnosed patients, and combined with radiation and chemotherapy.
Using the Immune System
Another approach to glioma treatment being examined is using the body’s own immune system to fight off the tumor. Researchers in a study took 19 patients with gliomas, made a vaccine for each one using his/her own tumor cells, and after the vaccination stimulated each person’s production of white blood cells (which fight off infection). Seventeen of the patients showed a response to the vaccine. In eight patients, the researchers could see the response on X-ray, and five of the patients actually improved. Some of the patients lived as long as two years after the treatment.
A possible treatment that received news coverage is the use of poliovirus to attack gliomas. Researchers discovered that the poliovirus has a natural attraction to a chemical that is found on malignant gliomas. However, since they didn’t want to cause polio, they used genetic engineering to take a piece of the virus that causes colds (rhinovirus) and put it in the poliovirus. This “deactivated” the disease-causing part of the poliovirus. The researchers created gliomas in mice, then tested the new virus on the tumors. They were excited to see that the tumors were eliminated. The next step will be designing a research study to test the virus in humans.