FRIDAY, July 15, 2005 (HealthDay News) -- There may be a "silver lining" for individuals who suffer from asthma or allergies: Scientists say genes that promote these disorders may also protect against a deadly brain cancer.
A recent study found that asthmatics and people with allergies are at lower risk of developing the most common type of brain tumor, glioblastoma multiforme.
"We found that four genetic variants on two different genes that increase susceptibility to asthma and other allergic conditions decrease the risk of the most common type of malignant brain tumor," said Judith Schwartzbaum, the lead author of the study and an associate professor of public health at Ohio State University.
Her team's findings appear in the July 15 issue of Cancer Research.
Each year, about 41,000 Americans are diagnosed with some form of brain tumor, according to the American Brain Tumor Association (ABTA), with glioblastomas accounting for about 23 percent of those cancers. Glioblastomas tend to be more common in men than in women, and are much more common in older vs. young people.
The average incidence is three cases of glioblastoma per 100,000 Americans, but after age 65 that number jumps to almost 14 per 100,000 people, according to the study authors. Just over three percent of patients diagnosed with glioblastoma will still be alive five years later.
The most common early symptoms are headache, nausea, vomiting and sleepiness, according to ABTA.
Schwartzbaum said past research has shown a possible link between asthma and allergies and a lower rate of brain cancer, but that the information was largely anecdotal and self-reported.
"I didn't believe that the connection between self-reported allergies and brain tumors was valid. That is why I looked at genetic variants," she said.
To see if there truly was a relationship between these disparate conditions, Schwartzbaum and researchers from Sweden, England and the United States compared DNA samples from 111 people with glioblastoma multiforme to samples from 422 age- and sex-matched healthy controls. All of the study volunteers were from Sweden.
The researchers looked for genetic variations known as polymorphisms on two genes known to be associated with asthma and allergies, IL-4RA and IL-13.
People with polymorphisms on those genes were more likely to have asthma and allergies and less likely to have a glioblastoma.
"For example, we found that one genetic variant that causes a two-fold risk in asthma susceptibility reduces the risk of glioblastoma multiforme by 40 percent," said Schwartzbaum.
Why genes that promote asthma or allergies might offer protection against brain tumors is unclear, said Schwartzbaum.
She speculated that the gene variations might hinder inflammation in the brain, even though those same genes help cause inflammation in the lungs.
The "cytokine genes that we looked at play a role in inflammation in allergy and asthma. But, surprisingly these cytokines also have anti-inflammatory properties. IL-13 inhibits cox-2 [enzyme] expression just like ibuprofen does, so it could possibly prevent the growth of blood vessels early in the development of a brain tumor," she said.
"This is an interesting observation that shows there are probably conditions that predispose one to illness that may be protective against other illnesses," said Dr. Jay Brooks, chair of hematology/oncology at Ochsner Clinic Foundation Hospital in Baton Rouge, La.
"From a practical standpoint, however, I don't think this study has clinical importance in telling people that they can prevent brain cancer," Brooks added.
Schwartzbaum said that, right now, her team's research shows an association only. No one knows whether the gene variations, some aspect of asthma/allergy treatment, or simply having asthma and allergies is behind the reduction in brain tumor risk, she said.
That's why individuals with asthma and allergies should continue to treat them as usual, she said. That's especially true for asthma.
"Asthma can be life-threatening so people with asthma need to treat it per their doctor's orders," she added.
To learn more about brain tumors, visit the National Institute of Neurological Disorders and Stroke.