Astrocytoma Tumors
August, 2005
Astrocytomas
are the most common glioma, accounting for about half of all
primary brain and spinal cord tumors. Astrocytomas develop from
star-shaped glial cells called astrocytes, part of the
supportive tissue of the brain. They may occur in many parts of the
brain, but most commonly in the cerebrum. They occur less commonly in
the spinal cord. People of all ages can develop astrocytomas, but they
are more prevalent in adults, particularly middle-aged men. Astrocytomas
in the base of the brain are more prevalent in children or younger
people and account for the majority of children’s brain tumors. In
children, most of these tumors are considered low-grade, while in adults
most are high-grade.
There are different types of astrocytomas, and these lesions are
classified into several categories according to their appearance under a
microscope. This classification is important because, the appearance of
an astrocytoma will often predict its behavior and, therefore, a
patient's prognosis.
Classification of Astrocytomas
Astrocytomas are generally classified (graded) into one of three
types: Low grade astrocytomas, anaplastic astrocytomas and
glioblastomas. Low grade astrocytomas account for 10 percent of
astrocytomas. These tumors are typically slow growing and may not
require specific treatment at the time of diagnosis. Many patients with
low grade astrocytomas live for prolonged periods of time after their
diagnosis. However, these tumors often advance into the higher grades
and more rapidly growing forms of brain gliomas. Anaplastic astrocytomas
and glioblastomas are the most aggressive and, unfortunately, the most
common astrocytomas. Glioblastomas are fast growing astrocytomas that
contain areas of dead tumor cells. In adults, glioblastoma occurs most
often in the cerebrum, especially in the frontal and temporal lobes of
the brain.
Symptoms
Symptoms vary depending on the location of the brain tumor, but may include any of the following:
- Persistent headaches
- Double or blurred vision
- Vomiting
- Loss of appetite
- Changes in mood and personality
- Changes in ability to think and learn
- New seizures
- Speech difficulty of gradual onset
In
early stages, children may experience headaches, nausea, vomiting,
blurred or double vision, dizziness, and changes in coordination.
Diagnosis
Sophisticated
imaging techniques can pinpoint brain tumors. Diagnostic tools include
computed tomography (CT or CAT scan) and magnetic resonance imaging
(MRI). Intraoperative MRI is also used during surgery to guide tissue
biopsies and tumor removal. Magnetic resonance spectroscopy (MRS) is
used to examine the tumor's chemical profile and determine the nature of
the lesions seen on the MRI. Positron emission tomography (PET scan)
can help detect recurring brain tumors.
Treatment Options
Treatment
options include surgery, radiation, radiosurgery, and chemotherapy. The
main goal of surgery is to remove as much of the tumor as possible
without injuring brain tissue needed for neurological function (such as
the ability to speak, walk, motor skills, etc.). However, high-grade
tumors often have tentacle-like structures that invade surrounding
tissues, making it more difficult to remove the entire tumor. If the
tumor cannot be completely removed, surgery can still reduce or control
tumor size. In most cases, surgeons open the skull through a craniotomy
to best access the tumor site. The goal of radiation therapy is to
selectively kill tumor cells while leaving normal brain tissue unharmed.
In standard external beam radiation therapy, multiple treatments of
standard-dose "fractions" of radiation are applied to the brain. Each
treatment induces damage to both healthy and normal tissue. By the time
the next treatment is given, most of the normal cells have repaired the
damage, but the tumor tissue has not. This process is repeated for a
total of 10 to 30 treatments, depending on the type of tumor. This
additional treatment provides some patients with improved outcomes and
longer survival rates.
Radiosurgery is a treatment method that
uses computerized calculations to focus radiation at the site of the
tumor while minimizing the radiation dose to the surrounding brain.
Radiosurgery may be an adjunct to other treatments, or it may represent
the primary treatment technique for some tumors
Patients
undergoing chemotherapy are administered special drugs designed to kill
tumor cells. Although chemotherapy may improve overall survival in
patients with the most malignant primary brain tumors, it does so in
only about 20 percent of patients. Chemotherapy is often used in young
children instead of radiation, as radiation may have negative effects on
the developing brain. The decision to prescribe this treatment is based
on a patient’s overall health, type of tumor, and extent of the cancer.
Before considering chemotherapy, you should discuss it with your
doctor, as there are many side effects.
Because traditional
treatment modalities are unlikely to result in a prolonged remission of
malignant astrocytomas, researchers are presently investigating a number
of promising new treatments including gene therapy, highly focused
radiation therapy, immunotherapy and novel chemotherapies. A number of
new treatments are being made available on an investigational basis at
centers specializing in brain tumor therapies.