History of allergies among adults with glioma and controls.

The causes of most adult gliomas are essentially unknown. Previous studies have indicated associations between immune system factors and the incidence of adult glioma, specifically that those individuals with certain allergic conditions may have decreased risk of glioma. We obtained detailed allergy histories for 405 adults newly diagnosed with glioma in the San Francisco Bay Area from 1997-1999 and 402 age-gender-ethnicity frequency-matched population-based controls. Seventy-nine percent of eligible cases or their proxies and 74% of eligible controls completed in-person interviews about allergies, age at onset, frequency, duration and severity. Overall, cases were less likely than controls to report any allergy (72% vs. 85%; odds ratio [OR] = 0.5 [0.3-0.7]); for self-reported cases (n = 269), OR = 0.7 (0.4-0.97) and for proxy-reported cases, OR = 0.3 (0.2-0.5). Pollen, dairy and nut allergies were significantly less common in cases than controls and most other allergens had odds ratios of less than one. There were no apparent trends with numbers of symptoms, route of exposure of allergen or reported severity of allergy, but there was a significant dose-response with increasing numbers of allergens (p < 0.0001 for linear trend among all cases vs. controls and p = 0.02 among self-reported cases only vs. controls). Although our work displays strong and consistent associations, future efforts must attempt to establish whether an immune system typified by proclivity to allergies, or an immunologic consequence of the allergies themselves, might be capable of preventing nascent brain tumors. The dominance of humoral immunity in the central nervous system is consistent with either of these models. Alternatively, common genetic or environmental causes for allergies and gliomagenesis may mediate or confound these observed inverse risks for allergies and gliomas, or other explanations may exist. Future work might reveal an important role for immunologic factors in gliomagenesis and potential preventative and/or therapeutic modalities.