Washington: New research has added to the growing body of evidence suggesting that there’s a link between allergies and reduced risk of a serious type of cancer that starts in the brain.
A new study has suggested that the reduced risk is stronger among women than men, although men with certain allergy profiles also have a lower tumour risk.
The study also strengthens scientists’ belief that something about having allergies or a related factor lowers the risk for this cancer.
Since these tumours, called glioma, have the potential to suppress the immune system to allow them to grow, researchers have never been sure whether allergies reduce cancer risk or if, before diagnosis, these tumors interfere with the hypersensitive immune response to allergens.
Scientists conducting this study were able to analyze stored blood samples that were taken from patients decades before they were diagnosed with glioma. Men and women whose blood samples contained allergy-related antibodies had an almost 50 percent lower risk of developing glioma 20 years later compared to people without signs of allergies.
“This is our most important finding,” Judith Schwartzbaum, associate professor of epidemiology at Ohio State University and lead author of the study, said.
“The longer before glioma diagnosis that the effect of allergies is present, the less likely it is that the tumor is suppressing allergies. Seeing this association so long before tumor diagnosis suggests that antibodies or some aspect of allergy is reducing tumor risk.
“It could be that in allergic people, higher levels of circulating antibodies may stimulate the immune system, and that could lower the risk of glioma.
“Absence of allergy is the strongest risk factor identified so far for this brain tumour, and there is still more to understand about how this association works,” Schwartzbaum said.
Many previous studies of the link between allergies and brain tumour risk have been based on self-reports of allergy history from patients diagnosed with glioma.
However, no previous studies have had access to blood samples collected longer than 20 years before tumour diagnosis.
The current study also suggested that women whose blood samples tested positive for specific allergy antibodies had at least a 50 percent lower risk for the most serious and common type of these tumours, called glioblastoma.
This effect for specific antibodies was not seen in men. However, men who tested positive for both specific antibodies and antibodies of unknown function had a 20 percent lower risk of this tumour than did men who tested negative.
Schwartzbaum and colleagues were granted access to specimens from the Janus Serum Bank in Norway. The bank contains samples collected from citizens during their annual medical evaluations or from volunteer blood donors for the last 40 years.
Norway also has registered all new cases of cancer in the country since 1953, and personal identification numbers enable cross-referencing those cases with previously collected blood samples.
The researchers analyzed stored samples from 594 people who were diagnosed with glioma (including 374 diagnosed with glioblastoma) between 1974 and 2007. They matched these samples for date of blood collection, age and sex with 1,177 samples from people who were not diagnosed with glioma for comparison.
They measured the blood samples for levels of two types of proteins called IgE, or immunoglobulin E. This is a class of antibodies produced by white blood cells that mediate immune responses to allergens.
Two classes of IgE participate in the allergic response: allergen-specific IgE, which recognizes specific components of an allergen, and total IgE, which recognizes these components but also includes antibodies with unknown functions.
In each sample, the scientists determined whether the serum contained elevated levels of IgE specific to the most common allergens in Norway as well as total IgE. The specific respiratory allergens included dust mites; tree pollen and plants; cat, dog and horse dander; and mold.
They then conducted a statistical analysis to estimate the association between elevated concentrations of allergen-specific IgE and total IgE and the risk of developing glioma.
Among women, testing positive for elevated levels of allergen-specific IgE was associated with a 54 percent decreased risk of glioblastoma compared to women who tested negative for allergen-specific IgE. The researchers did not see this association in men.
However, the relation between total IgE levels and glioma risk was not different for men and women, statistically speaking. For men and women combined, testing positive for elevated total IgE was linked to a 25 percent decreased risk of glioma compared with testing negative for total IgE.
The analysis for effects on glioblastoma risk alone suggested a similar decreased risk for both men and women combined whose samples tested positive for high levels of IgE, but the findings were considered borderline in terms of statistical significance, meaning the association could also be attributed to chance.
The study has been published online in the Journal of the National Cancer Institute.