The findings, while preliminary, could help advance the understanding of the immune system's role in cancer, researchers say.
The newly published study suggests that variations in specific genes that have been linked to asthma, hay fever, and other allergic conditions may also be associated with a decreased risk for the brain tumor known as glioblastoma multiforme.
Glioblastomas, or gliomas, are the most common type of brain cancers and are more common in the elderly. The tumor occurs in 13 out of 100,000 people over age 65, and the five-year survival rate in this age group is very low.
Genetic Link Explored
The study is not the first to suggest that people with allergies appear to have a lower risk of developing the deadly tumor. Researchers with the National Cancer Institute came to the same conclusion in a 2002 study that compared allergy history among people with and without gliomas.
The new study is the first, however, to show a possible genetic reason for the association.
Epidemiologist and researcher Judith Schwartzbaum, PhD, tells WebMD that people with two specific genetic variants for IL-4RA were twice as likely to have asthma but 40% less likely to have a glioblastoma. A similar association was seen for two variations on the IL-13 gene.
The study is published in the July 15 issue of the journal Cancer Research.
Is Inflammation the Key?
IL-4RA and IL-13 genes help regulate chemical messengers called cytokines, which control the actions of cells that drive the immune system.
Schwartzbaum says it is not yet clear if these chemicals play a direct role in the development of brain tumors or if allergies and gliomas share a common pathway within the immune system.
Another possibility, she says, is that the immune response that is triggered in people with asthma and allergies helps protect them against the brain cancer. This is just speculation, but Schwartzbaum says the implications of such an association would be great.
"If this is the case the question becomes, 'How aggressively should you treat these conditions?'" she tells WebMD. "Obviously, people can die from asthma. It is a serious disease that needs to be treated. But it could be that a little bit of hay fever may be a good thing."
So how could the same genetic variants promote one disease while protecting against another? Inflammation may hold the key, Schwartzbaum says. It turns out that the same cytokines that cause allergy- and asthma-promoting inflammation in the lungs inhibit inflammation in the brain. Less inflammation may mean less cancer risk.
NCI researcher Peter Inskip, ScD, was a co-researcher of the agency's 2002 allergy and brain cancer study. He tells WebMD that the link has now been seen in multiple studies, "which lessens the likelihood that it is due to chance or bias."
"We cannot rule out the possibility that allergies or asthma are directly protective," he says. "However, other possibilities should be considered. A possible protective role of medication taken for allergies and/or asthma needs to be evaluated further."
The NCI is continuing its research on allergies, asthma, and glioblastomas, he says.
"We know very little about the etiology of brain cancers, most of which are gliomas," he says. "The findings concerning allergies/asthma that have emerged over the last few years provide one of the most promising leads that we have. It is extremely important that researchers pursue this lead in order to better understand the biological basis of the association."