Glioblastoma is the most aggressive type of brain cancer, and it primarily strikes older adults, with a median age of diagnosis at 64. It affects about 3.2 people per 100,000 in the United States each year. While no single factor reliably predicts who will develop it, certain demographic traits, genetic conditions, and environmental exposures shift the odds.
Age, Sex, and Race
Risk rises sharply with age. Glioblastoma is uncommon in children and young adults, and incidence climbs steadily after age 50. Men develop it more often than women, though the reasons for that gap remain unclear.
Race and ethnicity also play a measurable role. White, non-Hispanic individuals have the highest incidence of any group, at roughly 4.7 per 100,000. That rate is about 2.5 times higher than in Black Americans, who have an incidence of around 1.8 per 100,000. Hispanic Americans fall in between at about 2.4 per 100,000, though within that group, white Hispanics are diagnosed nearly twice as often as Black Hispanics. Asian and Pacific Islander populations have the lowest incidence rates. These differences persist even after accounting for access to care and diagnostic imaging, suggesting that underlying genetic variation between populations plays some role.
Inherited Genetic Syndromes
The vast majority of glioblastomas appear without any identifiable inherited cause. But a small number of rare genetic syndromes substantially raise the risk. These syndromes involve mutations that are passed through families and increase vulnerability to multiple types of cancer, not just brain tumors.
- Li-Fraumeni syndrome is caused by a mutation in the TP53 gene, which normally acts as a brake on cancer growth. People with this syndrome face elevated risk for breast cancer, soft-tissue sarcomas, and glioblastoma.
- Lynch syndrome involves mutations in DNA repair genes. It is best known for raising the risk of colorectal and endometrial cancers, but it also predisposes people to glioblastoma and other brain tumors.
- Neurofibromatosis type 1 increases the risk of several types of glioma, particularly in children and young adults.
- Tuberous sclerosis and melanoma-neural system tumor syndrome also carry increased glioma risk, though these conditions are extremely rare.
If you have a family history of multiple cancers across generations, especially brain tumors combined with breast cancer, sarcomas, or colon cancer, that pattern could signal one of these syndromes. Genetic counseling can help clarify whether testing makes sense.
Prior Radiation to the Head
Moderate-to-high-dose ionizing radiation is the only firmly established environmental risk factor for brain tumors. This does not mean diagnostic scans like a single CT or dental X-ray. The risk comes from therapeutic radiation, the kind delivered to treat a previous cancer near the head or brain, particularly during childhood.
Children who receive radiation therapy to the head for an earlier cancer have a higher risk of developing a glioma years or even decades later. The association is stronger for people exposed at younger ages. Latency periods vary widely: some radiation-related brain tumors appear within 5 to 10 years, while others emerge 20 or 30 years after exposure. This is one reason childhood cancer survivors undergo long-term follow-up imaging.
Do Cell Phones Increase Risk?
Cell phones emit radiofrequency energy, a form of non-ionizing radiation that is too low-energy to damage DNA. Despite widespread concern, the evidence consistently shows no link between cell phone use and glioblastoma. Population-level studies in the United States, Nordic countries, and Australia have found stable glioma rates over the decades when cell phone use exploded. The largest case-control study on the topic (the Interphone study), a Danish cohort tracking subscribers for over 13 years, and a British cohort of more than 264,000 participants all reached the same conclusion: no increased risk, even among the heaviest and longest-duration users.
The World Health Organization’s cancer research arm classified radiofrequency fields as “possibly carcinogenic” in 2011, a category that reflects limited and inconclusive evidence rather than a confirmed danger. The National Cancer Institute’s current position is that the evidence to date does not support a causal link between cell phones and brain cancer.
Occupational and Chemical Exposures
Farming has been linked to a modestly higher rate of brain tumors in some studies. One large case-control study found that general farmers and farmworkers had roughly 2.5 times the odds of developing a glioma compared to non-farmers. However, when researchers looked specifically at pesticide exposure, including insecticides and herbicides, they found no consistent association with glioma risk in either men or women. That suggests something else about the farming environment, possibly exposure to animal viruses, dusts, or solvents, could explain the elevated rates rather than pesticides themselves.
Other occupational exposures that have been investigated include rubber manufacturing, petroleum refining, and vinyl chloride, but none have been established as definitive risk factors with the same confidence as ionizing radiation.
Allergies and a Surprising Protective Effect
One of the more counterintuitive findings in glioblastoma research is that people with allergies appear to have a lower risk. A large meta-analysis pooling data from 40 studies found that a history of any allergy was associated with a 29% reduction in glioma risk. People with asthma had an 18% lower risk, and those with eczema had a 16% lower risk. The protective effect was even stronger in people with two or more allergic conditions, who showed a 35% reduction compared to people without allergies.
This pattern was most pronounced for high-grade gliomas like glioblastoma, where the risk reduction reached about 41%. The leading theory is that an overactive immune system, the same kind that causes seasonal allergies and eczema, is better at detecting and destroying abnormal cells in the brain before they can form a tumor. This finding does not mean allergies prevent glioblastoma, but it does suggest that immune surveillance plays a meaningful role in who develops the disease.
What Most Cases Have in Common
For the majority of people diagnosed with glioblastoma, no identifiable cause is ever found. They have no relevant family history, no prior radiation exposure, and no unusual occupational background. The strongest predictors remain things no one can control: being older, being male, and being white. That is a frustrating answer, but it reflects the current state of the science. Glioblastoma appears to arise largely from the accumulation of random genetic errors in brain cells over a lifetime, with inherited and environmental factors tipping the balance in a small percentage of cases.