There may be one benefit to having a lot of allergies -- they may protect against glioma, researchers found.
Patients with gliomas were significantly less likely to report having any allergy (OR 0.60, 95% CI 0.46 to 0.79), a relationship that applied to both high- and low-grade tumors, Bridget McCarthy, PhD, of the University of Illinois at Chicago, and colleagues reported in the February issue of Cancer Epidemiology, Biomarkers & Prevention.
In fact, patients who had more types of allergies -- seasonal, medication, pet, food, and other -- had even lower odds of glioma, with an 11% reduction for those with allergies in one category and a 64% reduction for those with allergies in four or more categories (P<0.05 for trend).
The findings are compatible with previous studies, which have consistently observed an inverse relationship between allergies and the risk of brain tumors.
To further explore the associations between glioma risk and the duration and timing of allergies, as well as antihistamine use, McCarthy and her colleagues evaluated survey data from 419 patients with glioma (344 high-grade and 75 low-grade) and 612 hospital-based control patients who did not have brain tumors.
The patients came from two centers, Duke University Medical Center in Durham, N.C. and NorthShore University HealthSystem in Chicago.
After adjustment for age, race, gender, education, and site, patients with both high- and low-grade glioma were less likely to report having any allergy than the controls (OR 0.66 and 0.44, respectively).
Each of the five categories of allergies was associated with a lower likelihood of glioma overall -- seasonal (OR 0.55), medication (OR 0.68), pet (OR 0.60), food (OR 0.58), and other (OR 0.34).
Age at diagnosis and years since diagnosis of the allergy were not associated with the odds of having a glioma.
Oral antihistamine use was associated with a lower likelihood of having a high-grade tumor (OR 0.75, 95% CI 0.57 to 0.99), but not a low-grade tumor.
In an analysis restricted to antihistamines containing diphenhydramine hydrochloride, use of the medications was again associated with lower odds of having a high-grade glioma (OR 0.66, 95% CI 0.50 to 0.87), but not a low-grade tumor.
Further stratification found that the relationship was statistically significant only for those patients who did not have a medically diagnosed allergy.
From that, the researchers concluded that "antihistamine use, other than in relationship with allergy status, may not influence glioma risk."
The authors noted that further studies are needed to determine the biological mechanisms tying lack of allergy to the development of brain tumors -- if, in fact, the relationship is causal.
One proposed explanation involves enhanced immune surveillance in the presence of atopic disease that limits abnormal cell growth.
The researchers acknowledged some limitations of the study, including potential recall and selection bias, the low number of patients, particularly those with low-grade gliomas, and the possibility of an influence from factors that were not accounted for in the analysis.
The study supported by an NIH Specialized Programs of Research Excellence grant and by the American Brain Tumor Association.
The authors reported that they had no conflicts of interest.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
Cancer Epidemiology, Biomarkers & PreventionSource Reference: McCarthy B, et al "Assessment of type of allergy and antihistamine use in the development of glioma" Cancer Epidemiol Biomarkers Prev 2011; 20: 370-378.