Authors:
Deltour I, Johansen C, Auvinen A, Feychting M, Klaeboe L, Schüz J. Time Trends in Brain Tumor Incidence Rates in Denmark, Finland, Norway, and Sweden, 1974–2003. Journal of the National Cancer Institute. Ahead of print. December 3, 2009.

Background
The use of mobile phones in Nordic countries became widespread in the early 1990’s and sharply increased in the mid-1990’s. Time trends in brain tumor incidence may be indicative of possible associations with exposure to radiofrequency radiation from mobile phones.

Objective
The objective was to study time trends in brain tumor incidence in Denmark, Finland, Norway and Sweden for 1974 to 2003 and to evaluate whether these trends changed in 1998-2003, the period relevant for possible associations with an increase in brain tumor incidence due to previous exposure to radiofrequency field emitted from mobile phones.

Methods
The number of first primary brain tumors in patients aged 20 to 79 years by calendar year of diagnosis, 5-year age at diagnosis intervals and sex were obtained from the national cancer registries of the four Nordic countries. Information on the size of the population at risk by 5-year age groups for each calendar year was obtained from the national population registries. Glioma and meningioma were analyzed separately for men and women. Age-standardized incidence rates for these tumors were calculated using age distribution of the four countries in 1985 as the reference population. Annual incidence rates for the overall age range (20-79 years) and for the 20-year age groups (20-39, 40-59, 60-79 years) were analyzed using joinpoint regression models.

Results
The total number of brain tumors diagnosed from 1974 to 2003 was 59,984 among a population of 16 million. There was a gradual increase in the incidence rates of gliomas during the study period (0.5% per year among men and 0.2% per year among women) mainly due to the 60-79 year age group. Glioma incidence rates were stable in the age group 40-59 years, decreased slightly beginning from 1988 among men aged 20-39 years, and no trend was observed in 20-39 year old women. The incidence rate of meningioma increased by 0.8% per year in men and, after the early 1990’s, by 3.8% per year in women. The increasing trend in meningioma rates in women was driven by the 60-79 year age group with the largest number of cases.

Interpretation and Conclusion
No clear changes were observed in the long-term trends in the brain tumor incidence. The authors suggest several possible explanations for this finding: the induction period for brain tumors associated with mobile phone use may exceed 5-10 years; the risk may be too small to be observed; the risk may be restricted to subgroups of brain tumors or mobile phone users; there may be no increase in risk associated with mobile phone use. Studies of time trends in brain tumor incidence for longer periods are warranted.


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