What are brain tumors?

Brain tumors occur when cells in the brain begin to divide out of control and start to displace or invade nearby tissues. Large collections of this "out of control" tissue are called tumors. Occasionally, brain tumors can spread throughout the body. Tumors that have the potential to spread to other sites of the brain or body are called malignant. When tumors start in the brain, they are called primary brain tumors.

Any of the various normal cell types of the brain can mutate and become a primary tumor, and the particular cell type which makes up the tumor controls how the tumor is likely to behave. Brain tumors are not really thought of as a single disease, but rather as a collection of several diseases that are characterized by the cell type that makes them up, by how they behave, and by how they are treated. One of the special characteristics of brain tumors is that benign (non-cancerous) tumors in the brain can be just as bad as malignant (cancerous) brain tumors.

This is because the brain is such an important organ. It is locked into place by the skull and can't move out of the way if a tumor is growing near it. Even a benign tumor can cause pressure on the brain, and this pressure can be both symptomatic and life-threatening.

The brain is also a frequent site of metastases. Metastases are tumors which have spread from a cancer that started in a different body part; they do not start in the brain, but instead take up residence there after traveling from a separate cancer (like a lung cancer or breast cancer). These are not classified as primary brain tumors, but instead as brain metastases.

How are brain tumors classified?

Brain tumors are classified by the both the cell of the brain that makes them up, and how the tumor looks under a microscope. Primary brain tumors can arise from any of the cells in the brain. They can come from the neurons, the glial cells, the lining of the brain, or from specific structures in the brain. Metastases can travel from a variety of different cancer types. When a special type of doctor (called a pathologist ) looks at brain tumors under a microscope, he/she can get a sense of how aggressive the tumor is by the way the cells look.

Am I at risk for a brain tumor?

In the United States in 2005, it is estimated that there will be 18,500 new cases of primary brain tumors, and 12,760 deaths from primary brain tumors. For women, brain tumors represent the 10 th most common cause of cancer death, although they do not quite make the list of top 10 causes of cancer death for men. Brain tumors generally comprise about 1% of all newly diagnosed adult cancers.

Exposure to radiation has been linked to the development of certain types of primary brain tumors, especially if the exposure took place in childhood. Higher radiation doses are generally felt to increase the risk of eventually developing a brain tumor, and radiation-induced brain tumors can take anywhere from 10-30 years to form.

Although many chemicals have been shown to cause brain tumors in laboratory animals, there have never been any definite associations with chemical exposures proven in human beings. Chemicals that have been shown to cause brain tumors in animals include n-nitroso compounds, vinyl chloride, and certain solvents. However, when examining populations exposed to these various chemicals (like pesticide workers or workers in the petrochemical industry), there has never been any conclusive evidence to suggest that they get brain tumors at a higher rate than people without the chemical exposures.

Certain hereditary disorders can predispose someone to the development of certain brain tumors. Genetic diseases like neurofibromatosis type 1, neurofibromatosis type 2, von Hippel-Lindau disease, and tuberous sclerosis are all associated with an increased risk of developing a primary brain tumor.

With the recent popularity of cellular phones, many people have worried that their use may be a risk factor for developing brain tumors. However, there has never been any data to support this idea. In fact, a few studies have looked at this question and have always failed to show any correlation between cell phone use and brain tumors.

Because there are so many different types of brain tumors, there are different risk factors for developing each of them. To learn about the risk factors for developing a specific a specific type of brain tumor, please refer to the OncoLink overview on that particular cancer.

How can I prevent brain tumors?

Currently, there are no proven strategies to prevent the development of primary brain tumors. Studies of diets rich in anti-oxidants have not shown any benefits in terms of lowering the risk of developing primary brain tumors.

It is possible to decrease the risk of developing brain metastases from certain tumors by decreasing the risk of developing the initial primary tumor in the first place. Sometimes, when patients have certain cancers (ie: lung) that are well controlled, they will be offered preventive radiation therapy to the brain in order to decrease the likelihood of developing brain metastases in the future. This is called prophylactic cranial radiation. (Please see the section of this overview below for more information on radiation therapy.)

What screening tests are available?

Primary brain tumors are rare enough that they are not screened for with any specific tests. The best way to pick up a diagnosis of a brain tumor early is to see your doctor regularly for a thorough physical examination and to report any new, worrisome symptoms promptly. People with genetic disorders that predispose them for the development of primary brain tumors will often get periodic imaging studies of their brains to look for any evidence of abnormalities.

What are the signs of brain tumors?

Unfortunately, the very early stages of brain tumors may not cause any symptoms. As the tumor grows in size, it can produce a variety of symptoms, including:
 

• headache
• nausea
• vomiting
• loss of appetite
• seizures
• memory loss
• weakness
• visual changes
• problems with speech and language
• personality changes
• thought processing problems

Many of these symptoms are non-specific, and could represent a variety of different conditions; however, your doctor needs to see you if you have any of these problems. Because the brain controls so many different functions, the symptoms caused by brain tumors can be extremely variable. Headache is the most common symptom for patients with brain tumors, occurring in about 50% of cases.

How are brain tumors diagnosed and staged?

When a patient presents with symptoms suggestive of a brain tumor, the physician will perform a thorough history and physical examination. After that, the key to making the diagnosis is appropriate imaging.

Imaging can be performed with either a CT scan or MRI scan. A CT scan is a three dimensional x-ray, and patients will often be injected with a contrast agent to help visualize any abnormalities. CT scans are good tests because they are quick and easy to obtain, and will often be used as the first step towards making a diagnosis. However, an MRI scan is a better test for evaluating abnormalities in the brain. MRI scans utilize powerful magnets to make a three-dimensional picture. An MRI picks up finer detail than a CT scan, and is the study of choice to make the diagnosis of a brain tumor. MRI scans are usually obtained with the use of an injectable contrast agent as well.

For many types of brain tumors, the imaging characteristics are distinctive enough to give physicians a pretty good idea of the diagnosis. The primary management of most brain tumors is surgery. If imaging reveals that a mass suspicious for a brain tumor is in a surgically accessible spot, the patient is generally scheduled for surgery without any further diagnostic testing. After surgery, the specimen can be examined under the microscope by a pathologist, and a final diagnosis can be made. However, sometimes, tumors are not in a safe location for surgery. In those cases, in order to make a diagnosis, patients will often need a biopsy. A biopsy is a procedure where a small piece of the tumor is obtained using a needle under image guidance.

Primary brain tumors do not have a classic staging system the way most other cancers do. This is because the size of a brain tumor is less important than its location and the type of brain cell that makes it up. The likelihood of curing a brain tumor has to do with its location, the cell that makes it up, and how the tumor cells look under a microscope. Your doctor will give you a sense of how dangerous your tumor is and how it should be treated after weighing these factors.

Brain metastases are considered within the staging system of the cancer from which they originated. Thus, the presence of brain metastases automatically makes the primary tumor a stage IV cancer, because stage IV means the presence of any metastasis.

What are the treatments for brain tumors?

There are a number of different treatments for brain tumors. Most brain tumors are treated with a combination of multiple different types of therapy. The exact location and type of brain tumor will dictate which treatments are recommended.

Surgery

Surgical resection is recommended for the majority of brain tumors. It is rare that a primary brain tumor can be cured without a surgical resection. However, the location of the brain tumor will dictate whether or not surgery is an option. Some tumors are seated in places in the brain that are just too dangerous to operate on, and surgery cannot be employed. The risks to the patient from surgery depend on the location and size of the tumor. Talk to your neurosurgeon about the specific risks of your planned surgery.

Chemotherapy

Chemotherapy is the use of anti-cancer drugs that go throughout the entire body. These drugs may be given through a vein or with pills by mouth. One of the special challenges in treating brain tumors with chemotherapy is that there is a natural barrier between the brain and the blood, which blocks many medications from entering the brain. Only certain chemotherapy drugs can cross this blood-brain barrier to treat disease in the nervous system. One of the new ways that chemotherapy can be delivered for brain tumors is by implantation on a biodegradable wafer that is inserted by the neurosurgeon into the space left behind after surgery (called the tumor bed ). The chemotherapy wafer can then deliver high doses of chemotherapy to a localized area. Chemotherapy wafers are only approved for certain brain tumors, although future research may prove this approach useful for more diseases.

There are many different chemotherapy drugs used for brain tumors, and your medical oncologist can explain why he or she recommends one particular regimen over another in your case.

Radiation

Radiation therapy uses high energy rays (similar to x-rays) to kill cancer cells. Radiation can come from an external source (called external beam radiation therapy ), and it requires patients to come in 5 days a week for up to 6-8 weeks to a radiation therapy treatment center. The treatment takes just a few minutes, and it is painless. External beam radiation therapy is often employed for brain tumors, both as primary treatment for unresectable tumors and in addition to surgery.

Radiation therapy can also be given to a very focused area of the brain using a technique called stereotactic radiosurgery . Stereotactic radiosurgery requires a patient to have a head frame attached, so that a precise map can be made of the patient's head. Radiation is then focused from a variety of different angles to deliver a large radiation dose to the tumor or tumor bed. This can be performed using the same machine that delivers external beam radiation or by a special machine called a gamma knife.

Radiation can also be given internally by implanting high strength radioactive sources in the vicinity of the tumor or the tumor bed. This is called brachytherapy. Your radiation oncologist can answer questions about the utility, process, and side effects of the recommended radiation therapy in your particular case.

Follow-up testing

Once a patient has been treated for a brain tumor, he or she needs to be closely followed for a recurrence. At first, the patient will have follow-up visits fairly often. The longer he or she is free of disease, the less often he or she will have to go for checkups with examinations. The doctor will decide when to obtain follow-up MRI scans or PET scans.

Clinical trials are extremely important in furthering our knowledge of this disease. It is though clinical trials that we know what we do today, and many exciting new therapies are currently being tested. Talk to your doctor about participating in clinical trials in your area.

This article is meant to give you a better understanding of brain tumors. Use this knowledge when meeting with your physician, making treatment decisions, and continuing your search for information.