A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs.
But risk factors don't tell us everything. Having a risk factor, or even several, does not always mean that a person will get the disease, and many people get cancer without having any known risk factors.
Most brain tumors are not associated with any known risk factors and have no obvious cause, but there are a few factors that may raise the risk of brain tumors.
Radiation exposure
The best established environmental risk factor for brain tumors is radiation exposure, most commonly from some type of radiation therapy. For example, before the risks of radiation were recognized, children with ringworm of the scalp (a fungal infection) were sometimes treated with low-dose radiation therapy, which was later found to increase their risk of brain tumors as they got older.
Today, most radiation-induced brain tumors are caused by radiation to the head given to treat other cancers. This is most common in people who received radiation to the brain as children as part of their treatment for leukemia. These brain tumors usually develop around 10 to 15 years after the radiation.
These tumors are still fairly rare, but because of the increased risk (as well as the other side effects), radiation therapy to the head is only given after careful consideration of benefits and risks. For most patients with other cancers involving the brain or head, the benefits of radiation therapy far outweigh the risk of developing a brain tumor years later.
Family history
Most people with brain tumors do not have a family history of the disease, but in rare cases brain and spinal cord cancers run in families. In general, patients with familial cancer syndromes tend to have many tumors that first occur when they are young. Some of these families have well-defined disorders such as:
Neurofibromatosis type 1 (NF1)
This genetic disorder causes tumors to grow in the nervous system. People with this condition have higher risks of schwannomas, meningiomas, and certain types of gliomas, as well as neurofibromas (benign tumors of peripheral nerves). Changes in the NF1 gene cause this disorder. These changes are inherited from a parent in about half of all cases. In the other half, the NF1 gene changes occur before birth in people whose parents did not have this condition.
Neurofibromatosis type 2 (NF2)
This condition, which is much less common than NF1, is associated with vestibular schwannomas (acoustic neuromas) and, in some patients, meningiomas or spinal cord ependymomas. Changes in the NF2 gene are responsible for neurofibromatosis type 2. Like NF1, the gene changes are inherited in about half of cases or may occur before birth in children without a family history.
Tuberous sclerosis
People with this condition may have subependymal giant cell astrocytomas (low-grade astrocytomas that develop beneath the ependymal cells of the ventricles), along with benign tumors of the skin, heart, kidneys, and other organs. It is caused by changes in either the TSC1 or the TSC2 gene. These gene changes can be inherited from a parent, but in most cases they develop in people without a family history.
Von Hippel-Lindau disease
This condition is associated with an inherited tendency to develop benign or cancerous tumors in different parts of the body, including hemangioblastomas (blood vessel tumors) in the brain, spinal cord, or retina, as well as tumors of the inner ear, kidney, adrenal gland, and pancreas. It is caused by changes in the VHL gene. In most cases the gene changes are inherited, but in some cases the changes happen very early in life in people whose parents don't have them.
Li-Fraumeni syndrome
People with this condition are at higher risk for developing gliomas, along with certain other types of cancer. It is caused by changes in the p53 gene.
Other inherited conditions, including Gorlin syndrome, Turcot syndrome, and Cowden syndrome are also linked with increased risks of certain types of brain and spinal cord tumors. Other families may have genetic disorders that are not well recognized or that may even be unique to a particular family.
Immune system disorders
People with impaired immune systems have an increased risk of developing lymphomas of the brain or spinal cord. Lymphomas are cancers of lymphocytes, a type of white blood cell that fights disease. Lymphomas usually form in lymph nodes, which are small, bean-sized collections of lymphocytes found throughout the body. Primary lymphoma of the central nervous system is less common than lymphoma that develops outside the brain.
Deficiencies of the immune system may be congenital (present at birth), or they may be caused by treatments for other cancers, treatment to prevent rejection of transplanted organs, or the result of diseases such as the acquired immunodeficiency syndrome (AIDS).
Factors with uncertain, controversial, or unproven effects on brain tumor risk
Cell phone use
This has been the subject of a great deal of debate in recent years. Cell phones give off (emit) radiofrequency radiation, a form of energy on the electromagnetic spectrum between FM radio waves and those used in microwave ovens, radar, and satellite stations. Cell phones do not emit ionizing radiation, the type that damages DNA and can cause cancer. Still, there have been concerns that the phones, whose antennae are built-in and therefore are placed close to head when in use, might somehow raise the risk of brain tumors.
Some population-based studies have suggested a possible increased risk of brain tumors or of vestibular schwannomas with cell phone use, but most of the larger studies done to date have not found an increased risk, either overall or among specific types of tumors. Still, there are very few studies of long-term use (10 years or more), and cell phones haven't been around long enough to determine the possible risks of lifetime use. The same is true of any possible higher risks in children, who are increasingly using these phones. Cell phone technology also continues to change, and it's not clear how this might affect any risk.
These risks are being studied, but it will likely be many years before firm conclusions can be made. In the meantime, for people concerned about the possible risks, there are ways to lower exposure, such as using an earpiece to move the phone itself away from the head when used. For more information, see our document, Cellular Phones.
Other factors
Other environmental factors such as exposure to vinyl chloride (a chemical used to manufacture plastics), petroleum products, and certain other chemicals have been linked with increased risk in some studies but not in others. Exposure to aspartame (a sugar substitute), exposure to electromagnetic fields from power lines and transformers, and infection with certain viruses have been suggested as possible risk factors, but most researchers agree that there is no convincing evidence to link these factors to brain tumors. Research on these and other potential risk factors continues.
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