A new study has added to the growing body of evidence implying that there’s a link between allergies and reduced risk of a serious type of cancer that starts in the brain.
According to this particular study, published in the Journal of the National Cancer Institute, the reduced risk seems to be stronger among women than men, however men have a lower tumor risk with certain allergies.
Scientists have believed having allergies or similar factors reduces the risk for this cancer, and this study has strengthened that theory. Experts have never known whether allergies lower the risk of cancer or if, before diagnosis, these tumors (glioma) interfere with the hypersensitive immune response to allergens, because they have the potential to suppress the immune system in order to grow.
Stored blood samples that were taken from patients decades before they were diagnosed with glioma were analyzed by the researchers. The researchers found that there was a 50% reduced risk of developing glioma 20 years later for men and women who had blood samples containing allergy-related antibodies, compared to people without signs of allergies.
Judith Schwartzbaum, associate professor of epidemiology at Ohio State University, investigator in the University’s Comprehensive Cancer Center, and leading author of the study, said:
“This is our most important finding. 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 tumor, and there is still more to understand about how this association works.”
Studies, until now, have not been able to analyze blood samples collected longer than 20 years before tumor diagnosis. Previous studies examining the relationship between allergies and brain tumor risk have used self-report questionnaires on patients’ histories with glioma.
The study also showed that women had at least a 50% lower risk for the most severe and common type of these tumors, known as glioblastoma, if their blood samples tested positive for specific allergy antibodies. These results were not seen in men. On the other hand, men had a 20% reduced risk of this tumor if they tested positive for both specific antibodies and antibodies of unknown function than men who tested negative.
In the United States, glioblastomas constitute about 60% of adult tumors that start in the brain, which affects 3 in 100,000 people. Patients may seek treatments such as radiation, surgery, and chemotherapy. On average, these patients survive for about one year, with fewer than 25% surviving up to 2 years and just 10% surviving up to 5 years.
The Janus Serum Bank in Norway granted the research team access to specimens. This bank contains samples collected over the last 40 years from people during their annual medical checkups or from volunteer blood donors. Since 1953, Norway has registered all recent cancer cases in the country, and personal identification numbers allows cross-referencing those cases with blood samples that have been previously collected.
The experts were able to analyze stored samples from 594 citizens who were diagnosed with glioma, including 374 that were diagnosed with glioblastoma, between 1974 and 2007. These samples were matched for age, sex, and date of blood collection with 1,777 samples from people who did not have glioma in order to compare.
The team was looking for levels of two types of proteins, IgE, or immunoglobulin E, while they were measuring the blood samples. This is a class of antibodies that are made from white blood cells that mediate immune responses to allergens. Two classes of IgE take part in the allergic response:
- allergen-specific IgE- identifies specific components of an allergen
- total IgE- identifies these components but also includes antibodies with unknown functions
The researchers observed each sample and determined whether the serum had elevated levels of IgE specific to the most common allergens in Norway as well as IgE. Specific Respiratory allergens were:
- tree pollen and plants
- dog and horse dander
- dust mites
A statistical analysis was then conducted in order to approximate the association between the risk of developing glioma and elevated concentrations of allergen-specific IgE and total IgE.
A 54% reduced risk of glioblastoma was associated with the women who tested positive for elevated levels of allergen-specific IgE compared to the women who tested negative. This association was not seen in men.
The relation between total IgE levels and risk of glioma was the same for both sexes. For men and women combined, a 25% reduced risk of glioma was associated with testing positive for elevated total IgE.
The analysis for effects on glioblastoma risk alone showed a similar decreased risk for both men and women combined whose blood samples tested positive for elevated levels of IgE. However, this finding was considered borderline in terms of statistical significance because it was not a significant enough number, meaning there is still the possibility that the association could be caused by chance.
“There is definitely a difference in the effect of allergen-specific IgE between men and women. And even results for total IgE suggest there still may be a difference between the sexes. The reason for this difference is unknown,” explained Schwartzbaum.
This research has shown evidence for the likelihood that the immune system of people with respiratory allergies could help fight against this type of cancer. The author explained that being able to examine this association over 4 decades between blood sampling and tumor diagnosis gave him and his team better insight.
For example, a 46% reduced risk for developing glioma 20 years later was associated with a positive test for elevated concentrations of total IgE compared to samples that tested negative. That reduced risk was only about 25% in samples that tested positive for high levels of total IgE taken between 2 and 15 years before diagnosis.
“There may be a trend- the closer the samples get to the time of diagnosis, the less help the IgE is in decreasing the risk of glioma. However, if the tumor were suppressing allergy, we would expect to see a bigger difference in risk near the time of diagnosis.”
He hopes to further his research and analyze the serum samples for concentration of cytokines (chemical passengers that promote or suppress inflammation as part of the immune response) in order to see if these proteins play a part in the relationship between elevated IgE levels and reduced tumor risk.
Written by Sarah Glynn