Cancer can occur in the brain in one of two ways: as a primary tumor (one that originates in that area) or as a metastasis (a secondary tumor that spreads from a cancer elsewhere in the body). According to the American Cancer Society, about 21,810 people in the United States are diagnosed each year with brain tumors.
Types of Brain Tumors
“Tumor” is a general term for a swelling or new growth of tissue. Malignant tumors (sometimes called anaplastic tumors) contain most cells that are very different from normal cells; most benign tumors are made up of cells that are similar to normal cells. Brain tumors may be malignant or benign; however, because the brain is enclosed in the skull, even benign tumors can be dangerous. The skull cannot expand to make room for a growing tumor, so the tumor may press on or damage delicate brain tissue. Therefore, even a benign brain tumor may behave in a malignant fashion and become life-threatening. Some benign brain tumors can also eventually give rise to malignant cells. For these reasons, instead of “malignant” or “benign,” brain tumors are usually described as being “high grade” (rapidly growing) or “low grade” (slowly growing).
The World Health Organization recognizes 126 different types of central nervous system tumors. Most are defined according to the type of cells from which they arise. The most common of these tumors in adults are:
| Tumor Type & Origin |
Characteristics | Treatment Approaches | Incidence |
|---|---|---|---|
| Meningiomas Origin: Membranes lining the skull, covering the brain (meninges) |
Affects twice as many women as men; very rarely spreads | Often “watchful waiting;” if tumor grows surgery may be necessary | Accounts for 27 percent of primary brain tumors |
| High grade astrocytomas (glioblastomas, anaplastic astrocytomas) Origin: Supportive cells of the brain (astrocytes) |
Grows rapidly and invades nearby tissues | Surgery, radiation therapy, chemotherapy; many clinical trials are available | Accounts for about 25 percent of all primary brain cancers |
| Grade 1 and 2 Astrocytomas Origin: Supportive cells of the brain (astrocytes) |
Slow-growing; rarely spreads | Usually surgery or radiation therapy | Less than 10 percent of all primary brain cancers |
| Oligodendroglioma Origin: oligodendrocytes |
Often occurs in frontal or temporal lobe; can be high or low grade | Surgery, possibly radiation therapy and chemotherapy | Less than 3 percent of all brain cancers |
| Pituitary Tumors Origin: Pituitary epithelial cells |
May cause excessive secretion of hormones | Depending on tumor's location and hormonal effects, treatment ranges from surgery to radiation therapy to hormonal treatments | 6 percent of primary brain cancers |
| Schwannomas Origin: Cells that wrap around peripheral nerves (Schwann cells) |
Can cause reduced hearing and balance problems | Surgery when possible, then usually radiation | 7 percent of all central nervous system tumors |
| Primary Central Nervous System Lymphomas (CNS Lymphoma) Origin: Lymph tissue of the brain, spinal cord, meninges (outer covering of the brain), or eye (called ocular lymphoma) |
Develops most often in people whose immune systems are compromised, such as in people with AIDS | Chemotherapy and/or radiation therapy | 3,000 times more common in people with AIDS than in the general population (See AIDS-related Cancers) |
Meningiomas are the most common low-grade brain tumors in adults. They form from the membranes that line the skull and cover the brain, and are often curable with surgery. Glioblastomas, the most common high-grade brain tumors in adults, are probably the most resistant of all cancers to treatment. This is because this tumor type has “fingers” that spread very quickly and penetrate the folds of the brain, making glioblastomas very difficult to remove with surgery and radiation therapy. Oligodendrogliomas may sometimes be confused with malignant astrocytomas because their cellular makeup looks similar under the microscope, but patients with these tumors generally have a better prognosis and are more responsive to therapy.
Risk Factors
Most patients who develop a brain or spinal cord tumor have no clear risk factors. There are only two known environmental risk factors for developing a brain tumor:
- Exposure of the head to x-rays (not including dental x-rays) for the purpose of treating diseases such as cancer. This is seen in less than 5 percent of patients with brain cancer.
- A history of disorders of the immune system, including congenital immune deficiencies, AIDS, and immunosuppression to prevent rejection of transplanted organs or cells. These disorders increase the risk of lymphoma in the brain.
People with certain rare genetic disorders have an increased risk of some brain tumors: Li-Fraumeni syndrome increases the risk of glioma; von Hippel-Lindau disease increases the risk of hemangioblastoma; tuberous sclerosis increases the risk of astrocytoma; neurofibromatosis type 1 or “von Recklinghausen’s” disease increases the risk of glioma; and neurofibromatosis type 2 increases the risk of acoustic nerve tumor and meningioma.
Head trauma, exposure to petrochemicals, and consumption of aspartame has been cited as possible risk factors, but no link between these factors and brain tumors has ever been confirmed.
According to recent studies, cell phone use and the nonionizing radiation these phones emit are not risk factors for developing a brain tumor.
Symptoms
The brain is not a homogeneous, or uniform, organ — different parts of the brain govern different functions of the body, so symptoms of a brain tumor are usually related to the location of the tumor rather than to its size. Symptoms are caused by tissue destruction, compression of normal brain tissue by the tumor, swelling in the tissues around the tumor, or obstruction of the flow of fluid (called cerebrospinal fluid) around the brain and spinal cord.
Because symptoms reflect the tumor’s location, they can sometimes indicate where the tumor is located and what type of tumor it is. Symptoms of brain tumors (which are often the same symptoms for brain metastases) include:
- headache (when a tumor presses on surrounding brain tissue)
- nausea and vomiting
- seizures (a sudden, involuntary movement of the muscles)
- speech problems, impaired vision, weakness in parts of the body and trouble walking, general confusion (when a tumor affects these functional areas of the brain)
Because symptoms produced by a central nervous system tumor often resemble the symptoms of other diseases, careful evaluation and diagnosis are critical to determine the cause of these symptoms.
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