In a statistical model, the researchers compared the locations of residence of children who developed cancer at the age of 0-15 years during 1985-2015 (data from national Childhood Cancer Registry) with those of children from the general population (data from national censuses 1990, 2000 and 2010-15). Precisely geo-coded location data, so-called point data, were used for this purpose. In a previously published simulation study, the researchers showed the model using point data identifies areas of increased risk more accurately than other widely used models that rely on spatially aggregated data, such as the number of cases per community or district.
The analysis included 5,947 primary cancers, of which 1,880 (32%) were leukemias, 772 (13%) lymphomas, and 1,290 (22%) tumors of the central nervous system (CNS), i.e. tumors of the brain and spinal chord. The estimated local cancer rate deviated from the national average by up to -17% downwards and up to +13% upwards, depending on the location. The spatial variation was smaller for leukemias (-4% to +9%) and lymphomas (-10% to +13%), but larger for brain tumors (-18% to +23%).
The researchers found that the observed spatial variability could be partially accounted for by certain spatial indicators such as degree of urbanization or socio-economic position or by previously investigated environmental factors, namely traffic-related air pollution and natural background radiation. The factors considered accounted for 72% of the spatial variation observed for all cancers together, 81% and 82% for leukemias and lymphomas, and 64% for brain tumors.
A map displaying the results shows two regions with increased incidence of brain tumors, one in the north of the canton of Zurich (border area with the canton of Schaffhausen) and one in the so-called Seeland. The considered factors could not explain the increase rates of brain tumors observed in the two areas mentioned above. The researcher conclude that the search for environmental risk factors of brain tumors should be intensified and that various subgroups of brain tumors must be considered separately.
