We made a pooled analysis of two case-control studies on malignant brain tumours with patients diagnosed during 1997–2003 and 2007–2009. They were aged 20–80 years and 18–75 years, respectively, at the time of diagnosis. Only cases with histopathological verification of the tumour were included. Population-based controls, matched on age and gender, were used. Exposures were assessed by questionnaire.The whole reference group was used in the unconditional regression analysis adjusted for gender, age, year of diagnosis, and socio-economic index. In total, 1498 (89%) cases and 3530 (87%) controls participated. Mobile phone use increased the risk of glioma, OR = 1.3, 95%CI = 1.1–1.6 overall, increasing to OR = 3.0, 95% CI = 1.7–5.2 in the >25 year latency group. Use of cordless phones increased the risk toOR = 1.4, 95% CI = 1.1–1.7, with highest risk in the >15–20 years latency group yielding OR = 1.7, 95% CI = 1.1–2.5. The OR increased statistically significant both per 100 h of cumulative use, and per year of latency for mobile and cordless phone use. Highest ORs overall were found for ipsilateral mobile or cordless phone use, OR = 1.8, 95% CI = 1.4–2.2 and OR = 1.7, 95% CI = 1.3–2.1, respectively. The highest riskwas found for glioma in the temporal lobe. First use of mobile or cordless phone before the age of 20 gave higher OR for glioma than in later age groups.
There has been a large worldwide increase during th elast decade in the use of wireless communication, with greater exposure to radiofrequency electromagnetic fields (RF-EMF). This has caused increasing concern for health risk. During use of both mobile and cordless phones, the brain is the main target of RF-EMF. The highest exposure is on the same side of the brain when the handheld phone is used (ipsi-lateral), whereas the contralateral side is less exposed . Due to the smaller head size, thinner skull bones and higher brain conductivity, a child absorbs higher rates than adults [2–4]. Our group reported the first indication of an increased brain tumour risk associated with use of wireless phones some 15 years ago [5–7]. This was followed by additional case-control studies as reviewed in Hardell et al. . A Danish cohort study on mobile phone users has been initiated , but poor exposure assessment makes it uninformative [10,11].The International Agency for Research on Cancer (IARC) at WHO evaluated human cancer risks from RF-EMF exposure in May 2011. It included all sources in the frequency range of 30 kHz–300 GHz. A total of 29 invited scientists participated. The final classification as Group 2B means that RF-EMF exposure is ‘possibly’ a human carcinogen, a conclusion based on an overwhelming majority of the voting experts [10,12]. The evaluation on the long-term use of wireless phones, i.e. >10 years, were in the IARC classification based on our results [13–15] and the Interphone study group, also preprint studies available [16–18]. The brain tumours associated with the use of wireless phones are the malignant types, mostly glioma, and acoustic neuroma, a benign tumour of the 8th cranial nerve. In contrast, no consistent pattern of an association has been found for the most common benign braintumour, meningioma [see also reviews in [8,19,20]. The Inter-phone results were reported only on the use of mobile phones, whereas we also included cordless phones in our assessment.The potential bias due to this different classification of exposure that distorts of the overall risk towards unity has been discussed elsewhere [8,21].The IARC evaluation was based on fairly short latency period (time from first exposure until diagnosis), with results on at most the latency group ≥ 10 years. To study longer periods of use, we made a new case-control study encompassing patients diagnosed from 2007 to 2009. Data have already been published on acoustic neuroma , meningioma,  and malignant brain tumours in total . To enlarge the study group, we have now pooled our results on malignant brain tumours for 1997–2003 and 2007–2009, because the same methods were used for both periods. We present in the following results for the most common type o fmalignant brain tumour, glioma. It is of importance to present separate results on glioma to compare our results with Inter-phone . Also, separate analysis of other malignant brain tumour types is presented. The ethics committee approved these studies.
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