Causes and Risk Factors of Brain Tumors

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We don't know exactly what causes brain tumors, but some of the risk factors that have been identified include radiation exposure (both therapeutic and diagnostic), age, obesity, northern European ethnicity, pesticide exposure, and more. In addition, genetic factors may play a role, and those who have a family history of brain tumors, as well as those with certain genetic syndromes have a higher risk of developing the disease. There are also several possible risk factors, such as exposure to electromagnetic fields related to cell phone use, that are still being evaluated.

The role of environmental exposures, though not well understood at this time, deserves further research, as the incidence of brain tumors has been increasing significantly in industrialized countries.

brain tumor risk factors
Illustration by Verywell

Common Risk Factors

A risk factor is something that is associated with the development of a disease such as cancer but doesn't necessarily cause that disease. People who have a risk factor for developing a brain tumor won't necessarily develop one. Likewise, many people who develop brain tumors have no known risk factors for the disease. Most of the time, a cancer is caused by a combination of factors, something that is referred to as having "multifactorial" causes.

Knowing the risk factors, as well as the common signs and symptoms of brain tumors may help people identify the disease as soon as possible if it should occur. Some risk factors are "modifiable" meaning that measures can be taken to reduce risk, whereas others, such as your age, can't be changed. It can be helpful to be aware of risk factors so that you can make any needed changes, but at the same time, an understanding of risk factors shouldn't be used to judge people or talk about how they "caused" their tumor. If you have a loved one with a brain tumor they need you to simply love and support them, not to try and identify the possible causes. Nobody deserves a brain tumor, no matter what habits or lifestyle practices they have.

Risk factors can vary depending on the particular type of brain tumor, such as glioma, meningioma, astrocytoma, medulloblastoma, and more, and may include:

Age

Brain tumors occur most commonly in children and older adults, though they can occur at any age.

Sex

In general, brain tumors are more common in men than in women (around 70 percent more common). That said, one type of brain tumor, meningiomas, are more common in women than in men.

Race/Ethnicity/Socioeconomic Status

In the United States, white people are more likely to develop brain tumors than blacks. Around the globe, the incidence of brain tumors in higher in northern Europe than in Japan. People who have parents who were born in Sweden, in particular, have a roughly 21 percent higher chance of developing a brain tumor. We've also found that children born to mothers who have a high education level have a slightly increased risk.

Radiation Exposure

Exposure to radiation. either diagnostic (such as a CT scan or x-ray of the head), therapeutic (such as with radiation therapy to the head to treat leukemia, or when radiation was used to treat scalp psoriasis), as well as radiation related to atomic bomb blasts are associated with a higher risk of developing a brain tumor (gliomas and meningiomas).

The average amount of time between radiation therapy for cancer and the subsequent development of a secondary cancer is usually 10 to 15 years. We don't know how significant diagnostic radiation is with regard to brain tumor risk, but radiologists are practicing more caution when ordering CT scans, especially in young children.

A Personal History of Cancer

Both childhood cancers, and cancers such as non-Hodgkin's lymphoma, leukemia, and glioma in adults, are associated with an increased risk of developing brain tumors. It's not known if this is related to the cancer itself, treatments for the cancer (especially intrathecal chemotherapy, when chemotherapy drugs are injected directly into the cerebrospinal fluid that flows through the brain and spinal cord), or a problem (such as a gene mutation) that underlies both cancers.

HIV/AIDS

People who have HIV/AIDS have roughly double the risk of developing a brain tumor.

Overweight and Obesity

People who are overweight or obese (have a body mass index greater than 30) have an increased risk of brain tumors.

A History of Seizures

We know that having a seizure disorder has been associated with the development of brain tumors, but similar to the chicken and egg scenario, it's not certain whether having seizures increases risk, or if people with underlying tumors may have seizures related to the tumor before it is identified. There is also some thought that it could be the medications used to treat seizures that may raise the risk.

Some researchers have speculated that head injuries may be linked with brain tumors, but any clear association is unknown at this time.

Prenatal Factors

Prenatal birth weight, specifically a high fetal growth rate has been associated with a significantly increased risk of medulloblastomas, ependymomas, and one type of astrocytoma. The reason for this finding isn't certain, but researchers have hypothesized that conditions such as gestational diabetes (diabetes related to pregnancy) may play a role. Both children who are born large for gestational age (over 4500 grams or 9.9 pounds in a full-term infant) and small for gestational age (less than 2600 grams or 5 pounds 8 ounces in a full-term infant) or more likely to develop a brain tumor than children who are of normal size for age at birth.

There is some evidence that children born to mothers who eat cured meat (such as bacon, ham, pastrami, or pepperoni) during pregnancy, have an increased risk of brain tumors. In contrast, children whose mothers took a multivitamin during pregnancy appear to have a lower risk. In addition, there is a small amount of evidence that children born to mothers who eat a diet rich in fruits and vegetables during pregnancy have a lower risk. (If there is a risk related to eating too few fruits and vegetables, it's likely small, and parents of children who have brain tumors should not chastise themselves.)

Medications

The use of anti-inflammatory medications such as Advil (ibuprofen) has been associated with a reduced risk of brain tumors.

Pesticide Exposure

There is some evidence that exposure to insecticides used in the home, such as flea and tick products for animals, is associated with an increased risk of brain tumors in children and young adults. A 2013 review of 20 studies also seems to show that children born to parents who are exposed to pesticides on-the-job have an increased risk.

Occupational and Household Exposures

Many people are exposed to carcinogens (cancer-causing substances) at the workplace. Some occupations that have been linked with an elevated risk of brain tumors include firefighters, farmers, chemists, physicians, and those who work with petrochemicals, power generators, synthetic rubber manufacturing, or agricultural chemical manufacturing. It's not certain whether exposure to solvents, rubber, or vinyl chloride increases risk.

Air pollution and living near landfills are possibly associated with an increased risk.

Possible/Potential Risk Factors

There are a number of risk factors that are uncertain or for which studies have shown mixed results with an increased or decreased risk in some cases, but no change in risk in others. Some of these include:

Diet

As noted above, dietary habits during pregnancy (such as the consumption of cured meats, fruits, and vegetables), may be associated with the risk of brain tumors. Nitrosamines (formed in the body from nitrites and nitrates in cured meats, cigarette smoke, and some cosmetics) have been correlated with an increased risk of childhood and adult brain tumors, though the significance of the link remains uncertain.

Electromagnetic Fields

Electromagnetic fields, first of concern for those living near high voltage power lines (and still not clear), and now with the ubiquitous use of cell phones and other wireless devices, are possibly associated with an increased risk of brain tumors. Recently, a 2017 review of studies to date looking at the link between cell phone use and brain tumors found that long-term cell phone use may be associated with an increased risk of glioma, and the World Health Organization has labeled cellular phones as "possibly carcinogenic." Older analog phones were associated with the development of benign tumors known as acoustic neuromas. Recent studies have instead found a link between cell phone use and gliomas, the most common type of brain tumor.

With concerns such as this, it's important to discuss the latency period or the period of time between exposure to a carcinogen (cancer-causing substance or event) and the later development of cancer. It is because of this latency period that we may not know for decades the impact of a particular exposure. Cell phones have not been in use that long. In comparison, if cigarettes only became available a few decades ago we might be wondering whether they really increase the risk of cancer. Now it's very clear they do.

At the same time, people don't need to become fanatical and abandon their phones. For those who are concerned, especially parents who have children who use phones, the FDA suggests some steps you can take to reduce your exposure. These include:

  • Using the phone only for short conversations
  • Using a landline instead when available
  • Using a hands-free device to put more distance between the phone and your head. (With these devices, the source of energy in the antenna is not against the head.) Hands-free devices significantly reduce the amount of radiofrequency energy exposure.

As a final note, it could also be that electromagnetic fields work in conjunction with other exposures to increase risk. For example, exposure to petroleum products appears to increase brain tumor risk on its own, but exposures to solvents, lead, pesticides, and herbicides have been found to raise the risk of glioma primarily in people who are also exposed to at least moderate amounts of electromagnetic radiation.

Infections

Researchers have looked at the role of several infectious diseases relative to an increased or decreased risk of brain cancers. It has been found that having chickenpox as a child is associated with a lower risk of developing a brain tumor. The question is less clear when it comes to Epstein Barr virus infections (the virus that causes mono) and cytomegalovirus infections. While CMV has been found in the brains in people with brain tumors, and these infections may increase the risk of central nervous system lymphomas, it's not certain if there is any link with brain tumors.

Medical Conditions

For reasons unknown, having allergies as an adult has been associated with a lower risk of developing glioma. There appears to be a lower risk as well for people with allergic skin diseases (atopic dermatitis) such as eczema.

Smoking

Unlike many cancers that are associated with smoking, there is little evidence that smoking raises the risk of brain tumors such as gliomas and meningiomas. There is also little evidence that alcohol consumption plays a role in these tumors. A single older study found an increased risk in malignant gliomas in women who smoked marijuana, but not in men. In this study, the risk of gliomas was also increased for those who drank seven or more cups of coffee daily.

Genetics

Having a family history of brain tumors is associated with an increased risk of developing the disease, and it's thought that 5 percent to 10 percent of brain tumors are "hereditary" in nature. Having a first degree relative (mother, father, sibling, or child) with a brain tumor increases risk by a factor of 2.43.

There are also several genetic syndromes that are associated with an increased risk. Some of these include:

How a Brain Tumor Is Diagnosed
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