What You Should Know About Brain Cancer
Description of Brain Cancer
While primary brain cancer is relatively rare, there are, depending on classification, more than 20 types of brain tumors. Gliomas are the most common. They are cancers of the glial cells, which are interspersed between neurons and the vessels that supply the central nervous system with blood. As such, they perform metabolic functions in addition to serving as supportive cells to the nervous system. Approximately 80 percent of all gliomas and 40 percent of brain tumors are astrocytomas, arising from a glial cell called an astrocyte. Oligodendrogliomas, tumors of another supporting cell type in the brain, make up about seven percent of gliomas.
Non-glioma tumors originate in other cells of the central nervous system. Meningioma, for example, develops in the meninges surrounding the brain and spinal column. Usually benign, it is the most frequently occurring non-glioma cancer. It can be dangerous, however, if the tumor presses on the brain or spinal cord.
Gliomas are graded on the likelihood of their growing and spreading, from grade I, benign tumors, to extremely aggressive, grade IV tumors, such as glioblastoma multiforme, the most prevalent and deadly of astrocytomas. These are often described as non-infiltrating, infiltrating (low-grade or diffuse) and high-grade (infiltrating or diffuse anaplastic astrocytomas or glioblastomas).
In addition, other tumors can grow in the pituitary gland, in the midline of the brain, from the coverings of cranial nerves, and from many different endocrine, vasculature and supportive tissues.
The symptoms of brain tumors include frequent headaches, vomiting, mood and personality changes, changes in vision or speech, loss of coordination and seizures.
An estimated 20 percent of cancers – particularly lung and breast – spread to the brain, making it the most frequent site of metastasis.
Brain Cancer Statistics
An estimated 18,500 brain and spinal cord cancers will be diagnosed in 2005 in the United States, at least 85 percent of which will be brain tumors. Approximately 12,760 people will die from brain and spinal cord cancers this year, accounting for 1.4 percent of all cancers and 2.4 percent of all cancer deaths.
Brain tumors can affect individuals of all ages, with a brief peak in early childhood and a larger incidence spike in those 50 to 70 years old. They are the major cause of death in those under 15 years of age, and the third leading cause of cancer death in 15- to 34-year-olds.
The relative rate of survival five years after diagnosis varies with age and cancer type. Individuals with low-grade astrocytomas or oligodendrogliomas live an average of six to eight years. The average survival for glioblastoma is approximately one year. About 55 percent of all individuals ages 15 to 44 who develop a brain cancer live five years, whereas only 16 percent of those ages 45 to 64 do so. For those over 65, only five percent live five or more years.
Brain Cancer Diagnosis and Detection
No screening tests exist to detect brain cancer. Doctors suspect a brain tumor only when unexplained symptoms appear. Two types of imaging tests – magnetic resonance imaging (MRI) and computed tomography (CT) – mainly are used to diagnose brain tumors. CT creates detailed X-ray images, and MRI uses a large magnet to create radio waves; both require high-speed computers to construct detailed pictures.
If an imaging test indicates a high likelihood of a tumor, surgically removing a piece of cancerous tissue through a biopsy is the only way to make a definitive diagnosis.
Brain Cancer Prevention & Risk
Most brain tumors are not associated with any known risk factor and are impossible to prevent. One exception is the link between radiation and brain tumors. The most likely source of radiation exposure is from prior cancer treatment.
Latest Brain Cancer Research
Because glioblastoma is the deadliest and fastest-moving brain tumor – and the most common – many clinical research trials are aimed at patients with this cancer.
Some researchers are studying the drug Tarceva® (erlotinib HCL), which targets the epidermal growth factor receptor and is crucial to cell growth in many cancers, for recurrence of glioblastoma. Newer drugs directed against receptor and non-receptor signaling pathways are being investigated for their potential to limit tumor growth with minimal toxicity.
A number of research centers are testing novel agents, alone or in combination, that inhibit angiogenesis, cell proliferation and tumor cell migration. By selectively disrupting critical steps in the cell signaling pathway, more effective treatments for brain tumor patients may be possible in the future. Targeted therapies, which aim drugs at specific proteins or other molecules involved in the development of disease, may offer the best hope for brain cancer patients.
Gene therapy to date has not been successful; however, new approaches using viruses with limited capacity to replicate are being investigated. Vaccines and other approaches under study use various strategies to stimulate the body’s immune system to control tumor growth.
Brain Cancer Treatments
Tumors that originate in and metastasize to the brain are among the most difficult to treat. While surgery, radiation therapy and chemotherapy remain the mainstays of treatment for these cancers, they are far from perfect. Surgery can be difficult and risky if the tumor is near a vital portion of the brain. Chemotherapy agents have to find ways past the blood-brain barrier. Radiation can damage healthy tissue.
New radiation techniques are better able to avoid damaging normal tissue in treating brain cancer. Stereotactic radiosurgery entails delivering a single high dose of radiation directly to the tumor and not the surrounding, healthy tissue. It can be “fractionated,” or delivered in small daily doses for a period of time. Three-dimensional conformal radiation therapy uses a computer to create a model of the tumor and to determine the best radiation beam size, angle and dose. Intensity modulated radiation therapy varies the dose intensity of radiation, depending on the thickness of the tumor. In addition, physically depositing radiation into the tumor can be done either by direct radioactive “seed” implants (brachytherapy) or by implanting a “double lumen bag” with circulating radioactive substances (known as the “Gliasite technique”).
Surgery is the most common treatment for brain cancer (and frequently the only treatment for benign brain tumors). It is often extremely difficult to remove a brain cancer completely, given that it usually invades other, normal brain tissue as well. Still, neurosurgeons will attempt to remove as much of the tumor as possible, which sometimes can relieve symptoms. While in most cases benign, non-infiltrating astrocytomas can be cured by surgery alone, infiltrating astrocytomas also require radiation therapy. High-grade astrocytoma treatment typically also includes chemotherapy, and sometimes combinations of drugs.
Only three drugs are approved by the U.S. Food and Drug Administration for the treatment of malignant gliomas: BCNU, CCNU and temozolomide.