Association between glioma and history of allergies, asthma, and eczema: a case-control study with three groups of controls.

Because glioma etiology is largely unknown, the inverse association of glioma risk with atopic conditions is promising and deserves close scrutiny. We examined the association between a history of allergies, asthma, and eczema, and glioma risk using sibling, friend, and clinic-based controls. This analysis included 388 incident glioma cases and 80 sibling, 191 friend, and 177 clinic-based controls. Each subject's medical history was assessed via a Web-based or telephone survey. Odds ratios (OR) and their 95% confidence intervals (CI) for the associations with allergies, asthma, eczema, and the overall number of these conditions were calculated from conditional (for sibling and friend controls) and unconditional (for clinic-based controls) logistic models. Allergies were consistently inversely associated with the glioma: ORs were 0.53 (95% CI, 0.15-1.84), 0.54 (95% CI, 0.28-1.07), and 0.34 (95% CI, 0.23-0.50) with sibling, friend, and clinic-based controls, respectively. Asthma showed an inverse association only in the comparison with sibling controls (OR, 0.43; 95% CI, 0.19-1.00). Eczema showed an inverse association only in the comparison with friend controls (OR, 0.42; 95% CI, 0.15-1.18). The overall number of these conditions (ordinal score 0, 1, 2, 3) was inversely associated with glioma: The risk decreased 31% to 45% with each addition of an atopic condition. These estimates were the most stable when different control groups were considered. Comparing the prevalence of these conditions in the three control groups with published data, we note that clinic-based controls generally better approximate the prevalence data for population-based groups. These controls seem to present a reasonable choice for clinic-centered case-control studies.