A risk factor is anything that increases a person's 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, bladder, kidney, and several other organs. But having a risk factor, or even several, does not mean that a person will get the disease.

The majority of brain tumors are not associated with any risk factors. Most brain tumors simply happen for no apparent reason. A few risk factors associated with brain cancer are known.

Environmental Risk Factors

The only established environmental risk factor for brain tumors is radiation. Before the risks of radiation were recognized, children with ringworm of the scalp (a fungal infection) often received low-dose radiation therapy, which substantially increased their risk of brain tumors in later life.

Today, most radiation-induced brain tumors are caused by radiation to the head given for the treatment of other cancers. For this reason (as well as other side effects of radiation therapy), this treatment is only given after careful consideration of benefits and risks. For most patients with cancer involving the brain or other areas of the head, the benefits of radiation therapy far outweigh the risk of developing a second tumor years later.

Other environmental factors such as exposure to vinyl chloride (an odorless gas used in the manufacturing of plastics), petroleum products, and certain other chemicals have been associated with increased risk in some studies but not in others. Exposure to aspartame (a sugar substitute) and exposure to electromagnetic fields from cellular telephones or high-tension wires have been suggested as risk factors, but most researchers agree that no convincing evidence implicates these factors. In fact, several recent studies have found no connection between the use of cellular phones and brain tumors.

Immune System Disorders

People with impaired immune systems have an increased risk of developing lymphomas of the brain or spinal cord. Deficiencies of the immune system may be congenital (present at birth), may be a side effect of treatment for other cancers, may be a side effect of treatment to prevent rejection of transplanted organs, or may be the result of the acquired immunodeficiency syndrome (AIDS).

Lymphomas are cancers of lymphocytes, a type of cell of the immune system. Lymphomas usually form in lymph nodes. Primary lymphoma of the central nervous system is less common than lymphoma that arises outside the brain, but it is increasing in frequency even among individuals without an impaired immune system. The cause for this increase is not known.

Family History

Rare cases of brain and spinal cord cancers run in families. In general, patients with familial cancer syndromes have multiple tumors that occur when they are young. Some of these families have well-known disorders:

Neurofibromatosis type 2 is an inherited condition associated with schwannomas of both acoustic (hearing) nerves and, in some patients, multiple meningiomas or spinal cord ependymomas.

Patients with tuberous sclerosis (another inherited condition) may have noninfiltrating subependymal giant cell astrocytomas (low-grade astrocytomas that develop beneath the ependymal cells of the ventricles) in addition to benign tumors of the skin, heart, or kidneys.

Von Hippel-Lindau disease is associated with an inherited tendency to develop hemangioblastomas (blood vessel tumors) of the cerebellum or retina as well as renal cell (kidney) carcinomas.

Malignant brain tumors are rare in these disorders. Other families may have a genetic disorder that is not well recognized or that may even be unique to a particular family.

Revised 6-01