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Childhood brain tumours and use of mobile phones: comparison of a case–control study with incidence data
© Aydin et al.; licensee BioMed Central Ltd. 2012
Received: 2 April 2012
Accepted: 20 May 2012
Published: 20 May 2012
The first case–control study on mobile phone use and brain tumour risk among children and adolescents (CEFALO study) has recently been published. In a commentary published in Environmental Health, Söderqvist and colleagues argued that CEFALO suggests an increased brain tumour risk in relation to wireless phone use. In this article, we respond and show why consistency checks of case–control study results with observed time trends of incidence rates are essential, given the well described limitations of case–control studies and the steep increase of mobile phone use among children and adolescents during the last decade. There is no plausible explanation of how a notably increased risk from use of wireless phones would correspond to the relatively stable incidence time trends for brain tumours among children and adolescents observed in the Nordic countries. Nevertheless, an increased risk restricted to heavy mobile phone use, to very early life exposure, or to rare subtypes of brain tumours may be compatible with stable incidence trends at this time and thus further monitoring of childhood brain tumour incidence rate time trends is warranted.
As argued above, assuming a short latency of a few years, an increased brain tumour risk should be detectable in the incidence data that are already available today because of the steep increase in wireless phone use among adolescents during the last two decades (unless the risk is restricted to a very small subgroup of the population, e.g. very heavy mobile phone users). For this reason we restricted our analysis of cordless phone use to the first three years of use. Because most children and adolescents in CEFALO had used cordless phones earlier in life than mobile phones, we could address the effects of microwave radiation with longer latency time periods or with exposure at a young age. It is striking, however, that it was difficult for many participating families to recall the amount of cordless phone use early in life and some did not feel comfortable about answering questions about amount, duration, or years since first use. The seemingly inconsistent numbers in the tables are actually the consequences of missing answers to some of the questions [table six in the original paper ] or due to categories which were not mutually exclusive as explained in the footnotes in the original article [table four and five in the original paper].
Discussion and Conclusion
The original conclusions in the abstract and the last paragraph of our paper  were that “the absence of an exposure–response relationship either in terms of the amount of mobile phone use or by localization of the brain tumour argues against a causal association.” And “we cannot, however, rule out the possibility that mobile phones confer a small increase in risk and therefore emphasize the importance of future studies with objective exposure assessment or the use of prospectively collected exposure data.” Meanwhile, all available data from epidemiological studies should be evaluated and discussed in a balanced way, taking into account the strengths and limitations of each respective study design. Because of the well-described limitations of case–control studies with retrospectively assessed self-reported wireless phone use, it is imperative to check the consistency of the observed relative risk estimates with observed time trends of incidence rates to avoid drawing wrong conclusions [8, 9].
CEFALO study team
Tore Tynes, Tina Veje Andersen, Lisbeth Samsø Schmidt, Aslak Harbo Poulsen, Christoffer Johansen, Michaela Prochazka, Birgitta Lannering, Lars Klæboe, Tone Eggen, Daniela Jenni, Michael Grotzer, Nicolas Von der Weid, Claudia E. Kuehni.
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