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.