astrocytoma

(ăs'trō-sī-tō'mə)
n., pl., -mas, or -ma·ta (-mə-tə).
A malignant tumor of nervous tissue composed of astrocytes.

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Key Terms: Anaplastic, Biopsy, Glioma.

Definition

Astrocytoma is a tumor that arises from astrocytes, star-shaped cells that play a supportive role in the brain.

Description

The brain acts as a computer that controls all of the functions of the body. It stores information, memories, and with the use of hormones and electrical impulses, regulates and sends instructions to the rest of the body. Because of the brain's importance, cancers in the brain can affect many of the body's functions. The location of a tumor within the brain determines which effects it will have. Astrocytomas may occur in the cerebrum, the site of thought and language, the cerebellum, the area responsible for movement and muscle co-ordination, or the brainstem, the location that regulates critical activities like breathing and heartbeat. Childhood astrocytomas are most commonly located in the cerebellum, while adults usually develop astrocytoma in the cerebrum.

Astrocytomas rarely metastasize (spread) outside the brain to other parts of the body; however, they may grow and spread within the brain. As there is no extra room in the skull, the presence of a brain tumor causes an increase in intracranial (within the skull) pressure, resulting in headaches and possibly affecting normal brain function by compressing delicate brain tissue.

Astrocytomas are a type of glioma, a tumor of glial cells (specialized cells that give physical support and electrical insulation between neurons). They are sometimes called gliomas, anaplastic astrocytomas, or glioblastoma multiforme. Oligoastrocytomas are a type of mixed glioma similar to astrocytomas. They usually contain cells that originate from oligodendrocytes as well as astrocytes, and are usually low grade (grading is an estimate of the tumor's malignancy and aggressiveness; lower-grade tumors require less drastic therapy than high-grade tumors).

Demographics

Astrocytoma occurs slightly more often in males than in females. It is also slightly more common in Caucasians than in those of African or Asian descent. Although it affects both adults and children, children usually develop a less serious form with a better prognosis. The total incidence of all types of brain cancer, including astrocytomas, is approximately 13 people out of every 100,000.

Causes and Symptoms

The cause of astrocytoma is not known. Brain cancer may occasionally be caused by previous radiation treatments; however, x rays are not believed to play a role. As of 2001, studies have indicated that the moderate use of handheld cellular phones does not cause brain cancer; ongoing research will determine if long-term cellular phone use causes an increase in cancer incidence.

Some studies suggest that brain tumors may occur more frequently in people who have occupational exposure to certain chemicals, including some pesticides, formaldehyde, vinyl chloride, phenols, acrylonitrile, N-nitroso compounds, polycyclic aromatic hydrocarbons, lubricating oils, and organic solvents. The greatest risk is associated with exposure before birth or during infancy.

There is a slightly higher incidence of astrocytoma in the siblings and parents of people with this tumor; however, only one type of astrocytoma is known to have a genetic cause. The rare subependymal giant cell astrocytoma occurs in conjunction with tuberous sclerosis, a hereditary disorder.

A wide variety of symptoms develop as a result of astrocytoma including the following:

• headache
• nausea and vomiting
• neck stiffness or pain
• dizziness
• seizures
• unsteadiness in walking or unusual gait
• lack of coordination, decreased muscle control
• visual problems such as blurring, double vision, or loss of peripheral vision
• weakness in arms or legs
• speech impairment
• altered behavior
• loss of appetite

Because there are several different types of astrocytoma, not all patients will show the same symptoms. The location of the tumor within the brain will determine which symptoms a patient will experience. Because the tumor causes an increase in intracranial pressure, most people with astrocytoma will develop headaches and nausea and vomiting.

Diagnosis

In the first stage of diagnosis the doctor will take a history of symptoms and perform a basic neurological exam, including an eye exam and tests of vision, balance, coordination and mental status. The doctor will then require a computerized tomography (CT) scan and magnetic resonance imaging (MRI) of the patient's brain. During a CT scan, x rays of the patient's brain are taken from many different directions; these are combined by a computer, producing a cross-sectional image of the brain. For an MRI, the patient relaxes in a tunnel-like instrument while the brain is subjected to changes of magnetic field. An image is produced based on the behavior of the brain's water molecules in response to the magnetic fields. A special dye may be injected into a vein before these scans to provide contrast and make tumors easier to identify.

If a tumor is found it will be necessary for a neurosurgeon to perform a biopsy on it. This simply involves the removal of a small amount of tumor tissue, which is then sent to a neuropathologist for examination and staging. The biopsy may take place before surgical removal of the tumor or the sample may be taken during surgery. Staging of the tumor sample is a method of classification that helps the doctor to determine the severity of the astrocytoma and to decide on the best treatment options. The neuropathologist stages the tumor by looking for atypical cells, the growth of new blood vessels, and for indicators of cell division called mitotic figures.

Treatment Team

Treatment of astrocytoma will involve a neurosurgeon to remove the tumor, a neuropathologist to examine the tumor sample, and an oncologist to monitor the patient's health and coordinate radiation therapy and chemotherapy if necessary. Nurses and radiation therapists will also play a role. After treatment, the patient may be followed up by a neurologist to ensure that the tumor does not grow or recur.

Clinical Staging, Treatments, and Prognosis

There are several different systems for staging astrocytomas. The World Health Organization (WHO) system is the most common; it has four grades of increasing severity based on the appearance of the astrocytoma cells. Other methods of staging correspond fairly closely to the WHO system. Grades I and II are sometimes grouped together and referred to as low-grade astrocytomas. Over time, tumors may progress from a low-grade form with a relatively good prognosis to a higher-grade form and poorer prognosis. Additionally, tumors may recur at a higher grade.

Grade I Pilocytic Astrocytoma

This is also sometimes referred to as juvenile astrocytoma because it occurs more frequently in children than adults. Under a microscope, the astrocytes are thin and elongated, and known as pilocytes. They are accompanied by Rosenthal fibers. The tumor mass does not invade surrounding tissues and is sometimes enclosed in a cyst. In children, pilocytic astrocytoma often occurs in the cerebellum, but may also occur in the cerebrum.

Treatment of this grade depends on the patient's age and the location of the tumor. Surgery is the preferred treatment for this type of astrocytoma; it is performed by a procedure known as a craniotomy. An incision is made in the skin and an opening is made in the skull. After the tumor is removed, the bone is normally replaced and the incision closed. The neurosurgeon may also insert a shunt (drainage system) to relieve intracranial pressure; this involves inserting a catheter into a cavity inside the brain called a ventricle, then threading the other end under the skin to a drainage area where the fluid is absorbed.

If the tumor can be completely surgically removed, the patient may not need further therapy and may be monitored only for recurrence. If the tumor cannot be completely removed, patients may be given chemotherapy as well. If the tumor is not completely resected or if it continues to grow after chemotherapy, radiation therapy may be necessary. Radiation therapy is not normally given to children under the age of three in order to prevent permanent damage to the child's healthy brain tissue. Radiation treatment may cause swelling in the brain; steroids may be prescribed to reduce the swelling.

The best indicator for prognosis is complete removal of the tumor. With complete tumor removal, 80% of patients are alive ten years later. Location of the tumor in the cerebellum also suggests a better prognosis than other locations.

Grade II Low-Grade Diffuse Astrocytoma

These astrocytomas spread out and invade surrounding brain tissues but grow very slowly. Under the microscope, fibrous structures are present. Grade II astrocytomas may occur anywhere in the brain, in the cerebellum and brain stem, or in the cerebrum, including the optic pathways. Genetic studies indicate that mutations of the tumor suppressor gene p53 occur frequently in these tumors.

Surgical removal of the tumor is the first choice for treatment, but it may not be possible due the tumor's location. Surgery is usually followed by radiation. Patients under 35 years of age have a better prognosis than older patients; in older patients, low-grade tumors progress to higher grades more rapidly. Overall median survival is four to five years.

Pleimorphic xanthoastrocytoma, a tumor originating in cells of a mixture of glial and neuronal origin, is often considered a grade II astrocytoma. It is relatively benign and treated only with surgery.

Grade IIi Anaplastic Astrocytoma

Anaplastic astrocytoma occurs most frequently in people aged 50 to 60. The term anaplastic means that the cells are not differentiated; they have the appearance of immature cells and cannot perform their proper functions. Researchers believe this is due to a gradual accumulation of genetic alterations in these cells. These tumor cells invade surrounding healthy brain tissue.

Anaplastic astrocytomas may be inoperable because of their location and their infiltration into normal tissue; in this case radiation therapy is recommended. Chemotherapy may include various combinations of alkylating agents and other drugs, including carmustine, cisplatin, lomustine, procarbazine and vincristine. These tumors tend to recur more frequently than grade I and II tumors. Following treatment, median survival is 12 to 18 months. The five-year survival rate for these patients is approximately 10% to 35%.

Grade Iv Glioblastoma Multiforme

Glioblastoma Multiforme (GBM) is the most common primary brain tumor in adults. These tumors aggressively invade adjacent tissue and may even spread throughout the central nervous system. They frequently occur in the frontal lobes of the cerebrum. Tumor biopsies may show large areas of necrosis, or dead cells, surrounded by areas of rampant growth. There may also be a mixture of cell types within the biopsy. Genetic studies show that a number of different types of mutations can take place in genes for tumor suppressor p53 and other proteins that play a role in controlling the normal growth of cells.

Often GBM cannot be entirely surgically removed because it affects large areas of the brain. Radiation therapy will be given regardless of whether surgery is possible, except to very young children. Conventional radiation may be performed, but more specialized types, such as stereotactic radiosurgery, which uses imaging and a computer to treat the tumor very precisely, or interstitial radiation, which delivers radiation by placing radioactive material directly on the tumor, may also be used. Chemotherapy will follow radiation; it may include carmustine, lomustine, procarbazine, and vincristine.

GBM is most common in patients over 50 years of age and rarely occurs in patients under 30. Increasing age is associated with a poorer prognosis. Median survival is 9 to 11 months following treatment. Fewer than 5% of patients are alive five years later. Because of the poor prognosis of GBM, it is treated more aggressively than low-grade astrocytomas; many clinical trials take place to test new treatments.

Alternative and Complementary Therapies

While no specific alternative therapies have become popular for this particular type of brain cancer, patients interested in pursuing complementary therapies should discuss the idea with their doctor. A doctor may be able to provide information about the efficacy of certain techniques and whether they may interfere with conventional treatment.

Coping With Cancer Treatment

Patients may experience unpleasant side effects due to their treatment. Patients should discuss any side effects they experience with their doctors; occasionally an effect may be unexpected or dangerous and dosages may need to be adjusted. Doctors can help alleviate nausea with antinausea medications and may prescribe antidepressants to help the patient deal with the cancer on a psychological level. Joining support groups will also help patients deal with the psychological effects of treatment. Cancer survivors can help provide encouragement and offer advice for coping with cancer on a day-to-day basis.

Clinical Trials

Clinical trials are an important treatment possibility, especially for patients with tumors that are inoperable or do not respond well to treatment. Participation in clinical trials also gives patients an opportunity to make contributions to the search to find a cure for their cancer. A wide variety of clinical trials are available, particularly for the higher-grade astrocytomas. Trials for higher-grade astrocytomas may test new drugs, new combinations of drugs, drug implants, and higher doses of drugs, possibly in combination with different methods of radiation therapy. Some studies may examine the use of gene therapy or immune therapy, including vaccines.

Trials for lower-grade astrocytomas focus on finding chemotherapy that causes fewer side effects. Some studies may also feature new combinations of drugs while others may attempt to treat the tumor by using lower dosages of drugs spread out over a longer period of time.

Prevention

Currently, scientists do not know what causes the majority of brain cancers. There may be a slight genetic predisposition, as family members of astrocytoma patients have a slightly increased incidence of the disease. Clinical studies show that a large number of genetic alterations take place in the higher grade astrocytomas; although this helps to explain what is going wrong in the cells, it does not explain what is causing these genetic mutations to take place.

While it is known that ionizing radiation can cause brain tumors, most people are not exposed to this type of radiation unless they are being treated for cancer. Ongoing studies are examining the long-term risks of other types of radiation, but as of 2001, neither x rays, electromagnetic fields, or cellular phones appear to increase the likelihood of brain cancers.

Although evidence is not yet conclusive, some studies suggest that some brain tumors may be caused by environmental exposure to certain organic chemicals. Exposure is most harmful to the developing fetus and infants, so pregnant women may wish to consider whether they have any occupational exposure to organic chemicals. Parents of infants should be aware of pesticides and any other potentially harmful chemical their child could come into contact with.

Additionally there is some evidence that supplements containing vitamins A, C, E, and folate may have a protective effect when taken during pregnancy. The children of women who take these supplements during pregnancy are half as likely to develop brain tumors before age five.

Special Concerns

Children who develop astrocytoma should be monitored regularly by their physicians to ensure that the tumor does not recur. A follow-up schedule should be discussed with the doctor; the child may be examined twice a year initially, then tested annually afterwards. In addition to the possibility of recurrence, other health problems due to treatment may arise in the child. The child may have lower levels of growth hormone or thyroid hormone or delayed growth as a result of radiation. There may also be decreased intellectual capacity or learning or physical disabilities that can be detected during follow-up. Parents can then arrange for rehabilitation or special education for their child.

Questions to Ask the Doctor

• Where inside my brain is the cancer located and where will it spread?
• What types of treatment are recommended?
• What are the possible side effects of this treatment?
• How can the side effects be minimized?
• Am I eligible for any clinical trials?
• Are there any alternatives to this treatment?
• What are the chances that the cancer will return?
• Will this cause any disabilities?
• How will this affect my daily life?

Adults may also experience permanent negative effects as a result of their treatment. Radiation damage to healthy tissue may occasionally cause delayed effects such as decreased intellect, impaired memory, changes in personality, and confusion. These types of side effects should be reported to a health professional; the patient can be referred to rehabilitation specialists who can help with regaining abilities.

Resources

Periodicals

Inskip, Peter D., et al. "Cellular Telephone Use and Brain Tumors." New England Journal of Medicine 344 (2001): 79–86.

Pencalet, Phillipe, et al. "Benign Cerebellar Astrocytomas in Children." Journal of Neurosurgery 90 (1999): 265–73.

Yu, John S., et al. "Vaccination of Malignant Glioma Patients with Peptide-pulsed Dendritic Cells Elicits Systemic Cytotoxicity and Intracranial T-cell Infiltration." Cancer Research 61 (2001): 842–7.

Organizations

American Brain Tumor Association. 2720 River Rd., Des Plaines, IL 60018. (800) 886-2282. .

The Brain Tumor Society. 124 Watertown St., Suite 3-H, Watertown, MA 02472. (800) 770-8287. .

National Brain Tumor Foundation. 414 13th St., Suite 700, Oakland, CA 94612-2603. (800) 934-2873. .

Other

BRAINTMR T.H.E. Brain Trust. Electronic mailing list. [cited June 22, 2001]. .

—Racquel Baert, M. S.

A common intracranial tumor composed of astrocytes; classified in order of malignancy as differentiated or undifferentiated groups.

• gemistocytic a. — comprises gemistocytic astrocytes, plump or swollen astrocytes or gemistocytes.

n

A primary tumor of the brain composed of astrocytes and characterized by slow growth, cyst formation, invasion of surrounding structures, and often, the development of a highly malignant glioblastoma within the primary tumor mass.

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