Abstract
We investigated the relationship between childhood leukaemia and preceding history of allergy. A nationwide case–control study of childhood cancers was conducted in the United Kingdom with population‐based sampling of cases (n = 839) and controls (n = 1,337), matched on age, sex and region of residence. Information about clinically diagnosed allergies was obtained from primary care records. More than a third of subjects had at least one allergy diagnosed prior to leukaemia diagnosis (cases) or pseudo‐diagnosis (controls). For both total acute lymphoblastic leukaemia (ALL) and common‐ALL/precursor B‐cell ALL (c‐ALL), a history of eczema was associated with a 30% significant reduction in risk: the odds ratios (OR) and 95% confidence intervals (CI) were 0.70 (0.51–0.97) and 0.68 (0.48–0.98), respectively. Similar associations were observed for hayfever (OR = 0.47; 95% CI: 0.26–0.85 and OR = 0.62; 95% CI: 0.33–1.16 for ALL and c‐ALL, respectively). No such patterns were seen either for asthma and ALL, or for any allergy and acute myeloid leukaemia. A comparative analysis of primary care records with parents recall of allergy revealed only moderate agreement with contemporaneous clinical diagnoses for both cases and controls—confirming the unreliability of parental report at interview. Our finding of a reciprocal relationship between allergy and ALL in children is compatible with the hypothesis that a dysregulated immune response is a critical determinant of childhood ALL. © 2007 Wiley‐Liss, Inc.