Residential exposure to ultraviolet light and risk of precursor B-cell acute lymphoblastic leukemia: assessing the role of individual risk factors, the ESCALE and ESTELLE studies.

BACKGROUND: In a previous nationwide ecological study based on 20 years of registration and 7,443 cases of acute lymphoblastic leukemia (ALL), we reported a positive association between residential solar ultraviolet (UV) light at diagnosis and childhood precursor B-cell acute lymphoblastic leukemia (PBC-ALL). OBJECTIVE: The present study investigated the influence of suspected individual risk factors for ALL on the association between UV and PBC-ALL, and evaluated this association at the residence at birth. METHODS: Individual data collected by interviews in the ESCALE (2003-2004) and ESTELLE (2010-2011) nationwide case-control studies, which included 1,511 cases of leukemia aged less than 15 years and 3,102 population controls, were analyzed. Municipalities of residences at birth and at diagnosis/interview were extracted and assigned UV radiation exposure from the EUROSUN database. The potential confounders or effect modifiers considered were strongly suspected risk factors for ALL that were available in the ESCALE and ESTELLE studies. RESULTS: UV exposure at diagnosis was associated with PBC-ALL (OR = 1.27 [1.08-1.48]) for UV > 105.5 J/cm2 compared to UV ≤ 105.5 J/cm2. Considering exposure to UV at birth rather than at diagnosis/inclusion yielded almost identical results as both variables were strongly correlated. Taking into account the suspected ALL risk factors did not affect this association in the pooled study. CONCLUSION: Our findings suggest that our previous observation of an ecological association between residential UV radiation exposure at diagnosis and PBC-ALL was not confounded or modified by individual risk factors, and that the critical exposure time window may be prenatal.