Bayesian spatial modelling of childhood cancer incidence in Switzerland using exact point data: A nationwide study during 1985-2015.

Background: The aetiology of most childhood cancers is largely unknown. Spatially varying environmental factors such as traffic-related air pollution, background radiation and agricultural pesticides might contribute to the development of childhood cancer. We investigated the spatial variation of childhood cancers in Switzerland using exact geocodes of place of residence. Methods: We included 5,947 children diagnosed with cancer during 1985-2015 at age 0-15 from the Swiss Childhood Cancer Registry. We modelled cancer risk using log-Gaussian Cox processes and indirect standardization to adjust for age and year of diagnosis. We examined whether the modelled spatial variation of risk can be explained by ambient air concentration of NO2, natural background radiation, area-based socio-economic position (SEP), linguistic region, years of existing general cancer registration in the canton or degree of urbanization. Results: For all childhood cancers combined, the posterior median relative risk (RR), compared to the national level, varied by location from 0.83 to 1.13 (min to max). Corresponding ranges were 0.96 to 1.09 for leukaemia, 0.90 to 1.13 for lymphoma, and 0.82 to 1.23 for CNS tumours. The covariates considered explained 72% of the observed spatial variation for all cancers, 81% for leukaemia, 82% for lymphoma and 64% for CNS tumours. There was evidence of an association of background radiation and SEP with incidence of CNS tumours, (1.19;0.98-1.40) and (1.6;1-1.13) respectively. Conclusion: Of the investigated diagnostic groups, childhood CNS tumours show the largest spatial variation in Switzerland. The selected covariates only partially explained the observed variation of CNS tumours suggesting that other environmental factors also play a role.