Background: Some case-control studies have reported increased risks of glioma associated with mobile phone use. If true, this would ultimately affect the time trends for incidence rates (IRs). Correspondingly, lack of change in IRs would exclude certain magnitudes of risk. We investigated glioma IR trends in the Nordic countries, and compared the observed with expected incidence rates under various risk scenarios.
Methods: We analyzed annual age-standardized incidence rates in men and women aged 20 to 79 years during 1979–2008 using joinpoint regression (35,250 glioma cases). Probabilities of detecting various levels of relative risk were computed using simulations.
Results: For the period 1979 through 2008, the annual percent change in incidence rates was 0.4% (95% confidence interval = 0.1% to 0.6%) among men and 0.3% (0.1% to 0.5%) among women. Incidence rates have decreased in young men (20–39 years) since 1987, remained stable in middle-aged men (40–59 years) throughout the 30-year study period, and increased slightly in older men (60–79 years). In simulations, assumed relative risks for all users of 2.0 for an induction time of up to 15 years, 1.5 for up to 10 years, and 1.2 for up to 5 years were incompatible with observed incidence time trends. For heavy users of mobile phones, risks of 2.0 for up to 5 years' induction were also incompatible.
Conclusion: No clear trend change in glioma incidence rates was observed. Several of the risk increases seen in case-control studies appear to be incompatible with the observed lack of incidence rate increase in middle-aged men. This suggests longer induction periods than currently investigated, lower risks than reported from some case-control studies, or the absence of any association.
From the aSection of Environment and Radiation, International Agency for Research on Cancer, Lyon, France; bStatistics, Bioinformatics and Registry Unit, Danish Cancer Society Research Center, Copenhagen, Denmark; cDepartment of Epidemiology, Tampere School of Public Health, University of Tampere, Tampere, Finland; dResearch and Environmental Surveillance, STUK - Radiation and Nuclear Safety Authority, Helsinki, Finland; eUnit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; fSurvivorship Unit, Danish Cancer Society Research Center, Copenhagen, Denmark; gDepartment of Radiation Protection and Nuclear Safety, Norwegian Radiation Protection Authority, Østerås, Norway; and hThe Cancer Registry of Norway, Oslo, Norway; and iInstitute for Statistical and Epidemiological Cancer Research, Finnish Cancer Registry, Helsinki, Finland.
Submitted 21 April 2011; accepted 20 October 2011; posted online 16 January 2012.
Supported by the Danish Strategic Research Council (grant number 2064-04-0010).
The simulations used data collected for the Interphone study in Denmark, Finland, Norway, and Sweden. The Interphone study was supported by funding from the European Fifth Framework Program, ‘Quality of Life and Management of Living Resources’ (contract QLK4-CT-1999901563) and the International Union against Cancer (UICC). The UICC received funds for this purpose from the Mobile Manufacturers' Forum and GSM Association. Provision of funds to the Interphone study investigators via the UICC was governed by agreements that guaranteed Interphone's complete scientific independence. The terms of these agreements are publicly available at http://www.iarc.fr/en/research-groups/RAD/RCAd.html.
The authors reported no other financial interests related to this research.
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Correspondence: Isabelle Deltour, Section of Environment and Radiation, International Agency of Research on Cancer, 150 Cours Albert Thomas, 69008 Lyon, France. E-mail: firstname.lastname@example.org.