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Many types of tumors can start in the brain or spinal cord. Different tumors are unlikely to all have the same causes, but they might share some things in common. Learn about the causes and risk factors for brain and spinal cord tumors and whether there are things that can help lower your risk.

What causes brain tumors in adults?

The exact cause of most brain and spinal cord tumors is not fully understood, and there are very few well-established risk factors. But researchers have found some of the changes that can occur in normal brain cells that lead them to form brain tumors.

All tumors start because of changes in genes (DNA) that control how cells grow and divide. In most cases, these genetic changes happen by chance during a person’s lifetime, not because they were inherited. It is very rare for brain cancers to run in families or be passed down through a cancer-causing gene.

Gene changes in brain tumors

Researchers have made great progress in understanding how certain gene mutations (changes) can cause normal cells to become cancer cells. For example, some genes control when cells grow and divide. Changes in these genes can lead to the development of cancer. Changes in several genes are usually needed before brain cells form tumors.

There are many kinds of brain tumors, each of which may have different sets of gene changes. A number of gene changes have been found in different brain tumor types, but there are probably many others not yet found.

Inherited vs. acquired gene changes

Gene changes can either be inherited from a parent or acquired during a person’s life.

Some rare inherited syndromes increase the risk of developing some brain and spinal cord tumors. For example, Li-Fraumeni syndrome involves changes in the TP53 tumor suppressor gene, which normally helps prevent cells with damaged DNA from growing. Changes in this gene increase the risk of brain tumors (particularly gliomas), as well as some other cancers.

However, most brain tumors result from gene changes acquired during a person’s life, not inherited. In most cases it's not clear why these changes happen.

What causes gene changes in the brain?

It’s still not clear what causes most gene changes that lead to brain tumors. The brain is fairly well protected from most cancer-causing chemicals in food or air, so these are unlikely to play a major role. Other than radiation, no known lifestyle-related or environmental factors are clearly linked to brain tumors.

Many of the gene changes in brain tumor cells might just be random events that happen inside a cell, without having an outside cause.

Risk factors for brain tumors

A risk factor is anything that increases your chances of getting a disease such as a brain tumor. Many types of tumors can start in the brain or spinal cord. While they have some things in common, they might not all have the same risk factors.

Most brain tumors are not linked with any known risk factors and have no obvious cause. But there are a few factors that can raise the risk of brain tumors.

Keep in mind that having a risk factor, or even several, doesn’t always mean that a person will get the disease. Some risk factors, such as your age or inherited genetic syndromes, cannot be changed. But in some cases, there may be ways to lower your risk.

Radiation exposure

The only known environmental risk factor for brain tumors is radiation exposure, most often from radiation therapy. For example, radiation given to the head to help treat another cancer (such as leukemia) can increase the risk of getting a brain tumor later on. These brain tumors most often develop around 10 to 15 years after the radiation, but sometimes they might not appear until decades later.

Radiation-induced brain tumors are rare. But because of the increased risk (as well as other side effects), doctors only give radiation therapy to the head after carefully weighing the possible benefits and risks. For most people who need radiation therapy to the head to treat their cancer, the benefits far outweigh the increased risk of developing a brain tumor years later.

The possible risk from exposure to imaging tests that use radiation, such as x-rays or CT scans, is not fully known. These tests use much lower doses of radiation than radiation therapy treatments, so if there is any increase in risk, it is likely to be very small. But to be safe, doctors typically recommend these tests only when clearly needed (especially for children or during pregnancy).

Certain inherited genetic syndromes

Most people with brain tumors don’t have a family history of them, but in rare cases brain and spinal cord tumors do run in families. Most often this is part of a family cancer syndrome, where family members share a gene change that increases their risk for several types of cancer or tumors. In general, people with family cancer syndromes tend to have many tumors that first occur when they are young.

Examples of family cancer syndromes that increase the risk for brain tumors include:

Having a weakened immune system

People with weakened immune systems have an increased risk of developing lymphomas of the brain or spinal cord (known as primary CNS lymphomas). Lymphomas are cancers of lymphocytes, a type of white blood cell that fights disease. Primary CNS lymphoma is less common than lymphoma that develops in other parts of the body.

A weakened immune system can be congenital (present at birth), or it can be caused by treatments for other cancers, treatment to prevent rejection of transplanted organs, or diseases such as AIDS (acquired immunodeficiency syndrome).

Do cell phones cause brain tumors?

Cell phones give off a type of non-ionizing radiation called radiofrequency (RF) rays. Unlike ionizing radiation (such as x-rays), RF energy does not damage DNA and is not known to cause cancer.

Still, because cell phones have internal antennae and are held close to the head, some people have worried that they might raise the risk of brain tumors.

Some studies have suggested a possible increased risk of brain tumors such as vestibular schwannomas (acoustic neuromas) with cell phone use. However, most of the larger studies done so far have not found an increased risk, either overall or among specific types of tumors.

The possible risks of cell phones are still being studied. For people concerned about the possible risks, you can lower your exposure by using the phone's speaker or a hands-free device to keep the phone away from your head. 

For more on this topic, see Cellular Phones.

Other factors with uncertain, controversial, or unproven effect on brain tumor risk

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 an increased risk of brain tumors in some studies but not in others.

Some research has suggested that trauma to the head might increase the risk of brain tumors. This is an ongoing area of research.

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 possible risk factors continues.

Can brain tumors in adults be prevented?

The risk of many cancers in adults can be reduced with certain lifestyle changes (such as quitting smoking). But other than radiation exposure, there are no known lifestyle-related or environmental risk factors for brain and spinal cord tumors, so at this time there is no known way to prevent most of these tumors.

Limiting radiation exposure to the head

For many people with other types of cancer in or near the head, the benefits of radiation therapy will outweigh the small risk of developing a brain tumor years later. Even then, doctors try to limit the dose of radiation as much as possible.

Imaging tests such as x-rays or CT scans use much lower levels of radiation than those used for cancer treatment. If there is any increase in risk, it is likely to be very small. But to be safe, doctors typically recommend these tests only when clearly needed (especially for children or during pregnancy).