Birth Order, Atopy, and Risk of Non-Hodgkin Lymphoma

Background: Immune defi ciency is a strong risk factor fornon-Hodgkin lymphoma (NHL), but whether or not otherforms of immune dysregulation are associated with NHL riskis unknown. We investigated associations between atopy,which is associated with a Th2-dominant immune response,and NHL risk. Because late birth order and childhoodcrowding are inversely associated with atopy, we also investigatedtheir associations with NHL risk. Methods: We carriedout a population-based case-control study among adults aged20 – 74 years in New South Wales and the Australian CapitalTerritory, Australia. NHL patients without clinically apparentimmune defi ciency (N = 704) were selected from a cancerregistry, and control subjects (N = 694) were randomlyselected from state electoral rolls and frequency-matched tocase patients by age, sex, and area of residence. Birth order,childhood crowding, and history of atopic conditions (hayfever, asthma, eczema, and specifi c allergies) were assessedby questionnaire and interview. Odds ratios (ORs) and 95%confi dence intervals (CIs) were calculated from logisticregression models that included the matching variables ascovariates. Results: The odds ratios for developing NHLwere 0.52 (95% CI = 0.32 to 0.84) for only children, 0.55(95% CI = 0.40 to 0.75) for fi rst-born children, 0.70 (95%CI = 0.51 to 0.96) for second-born children, and 0.81 (0.57 to1.14) for third-born children (all compared with fourth- orlater-born children) ( P trend