Cancer is one of the most common causes of disease and death globally. The causes for initiation and tumor progression of malignant tumors (carcinogenesis) are known in some cases (e.g., asbestos or smoking for lung cancer), however they are not yet often discovered despite intensive research.
In the lower range of the electromagnetic spectrum, Wertheimer and Leeper observed an increased incidence of childhood leukemia in the vicinity to 50/60 Hz magnetic fields of power transmission lines in 1979. This finding initiated several studies in different countries for further investigation of the possible association by applying different methods of exposure assessment. The overall conclusion based on the results of the partly contradicting studies was that the risk for childhood leukemia was possibly twice as high for exposure to a magnetic field with a long-time average of 0.4 microTesla. In 1999 the International Agency for Research on Cancer (IARC) classified extremely low frequency magnetic fields as "possible human carcinogen" (Group 2B) in the same group as caffeine although there was no known biological mechanism despite intensive laboratory research.
The carcinogenic effects of ionizing radiation such as UV, X-rays and gamma radiation ranging in the upper part of the electromagnetic spectrum were investigated and verified in experimental and epidemiological studies. Based on the evidence of these findings, the IARC classified ionizing radiation as "carcinogenic to humans" (Group 1).
The exponentially increasing use of mobile phones in the past 15 years and the undisclosed effects of extremely low frequency magnetic fields led to the investigation of possible effects of the waves in the middle part of the electromagnetic spectrum used in mobile communication. If the use of a mobile phone would increase the risk for cancer, then a large number of humans worldwide would be affected. Therefore, a large number of studies were initiated: 1. medical/biological studies to disclose the possible action mechanism of mobile communication exposure on organisms under standardized laboratory conditions and to supply proven results concerning a possible association, and 2. epidemiological studies to investigate the possible association between mobile phone use and cancer incidence within the population.
Since the mobile phone is held next to the ear during a call, and this area of the head is mostly exposed, brain tumors of the adjacent tissues are investigated. These brain tumors are glioma, meningioma, and acoustic neurinoma. In 1999, the International Agency for Research on Cancer (IACR) initiated the Interphone project to investigate these rarely occurring tumor types. Case-control studies were conducted in Germany, Denmark, Finland, Norway, Sweden, France, Italy, UK, Israel, Australia, New Zealand, Japan, and Canada following a common core protocol. The aim was to gain a large number of cases of the rare tumors and to analyze the results of all countries combined.
There are several methodological limitations of epidemiological studies on neurodegenerative diseases. First of all, these diseases are not recorded in national registries compared to cancer registries. Therefore mortality registries are used for data on cause of death and occupation, these data are less informative than patient records (WHO, 2007"). Furthermore, in some of the studies the categorization into electrical occupations is based on the job title and for this reason it is not very precise. In more recent studies, exposure assessment was improved by applying a job exposure matrix which is based on measured magnetic flux densities in the work places of different occupations (e.g. Theriault et al (1994), Floderus et al (1996) and Bowman et al (2007)).
Electric shocks have been discussed as possible confounder in studies on electric occupations (Kheifets et al, 2009). Whether the workers in electrical occupations have received electric shocks is only included in a few studies on the exposure to magnetic fields and neurodegenerative diseases. Other risk factors which have not been considered, could be the effects of chemicals in the workplace.
The incidence of brain tumors is quite low with a proportion of 2 % of all cancer types. 3 to 5 per 100,000 persons are diagnosed with a brain tumor each year. In contrast to well-defined exposure setups in medical/biological studies, no measured values are available for exposure assessment in epidemiological studies. The amount of individual exposure is retrospectively assessed by questionnaires about the calling habits. Memory and cognitive function may be impaired by the growing brain tumor. Furthermore, an ill person may overestimate the number and duration of calls due to cogitation of the possible causes of the cancer in comparison to a healthy individual (recall bias). The latency of brain tumors, that is the time until the first symptoms appear, is often longer than the investigated time period of mobile phone use which is only in some cases more than 10 years. Therefore, no conclusion can be drawn to the long-term effects of mobile phone use for the initiation and development of brain tumors.
The results of several Interphone project participating countries are already published. The overall analysis of the results of all countries is still pending. No association between brain tumors and mobile phone use for less than 10 years was found in the published results. This observation is in contrast to the results of the Swedish research group of Hardell. The number of long-term users in the Interphone study is low, therefore an unambiguous statement cannot be made.
The aim of the CEFALO study is to investigate whether the use of mobile phones increases the risk of developing brain tumors in children and adolescents in the age group 7-19 years. The multinational case-control studies were conducted in Denmark, Sweden, Norway and Switzerland in the time period 2004 to 2008. The results will be published at the end of 2009.
In 2008, the international cohort study of mobile phone use and health (COSMOS) was initiated as a long-term project to investigate the possible association between long-term mobile phone use and adverse health effects. The five European countries of the UK, Denmark, Sweden, Finland, and the Netherlands participated in study.
The international multi-centre MOBI-KIDS study was initiated in 2009 to investigate the relationship between communication technologies including mobile phones factors and brain cancer in young people. Over a study period of five years, nearly 2000 young people between 10 to 24 years with brain tumours and a similar number of young people without a brain tumour will be invited to participate in the study. Research groups of following countries are involved from the start: Australia, Austria, Canada, France, Germany, Greece, Israel, Italy, New Zealand, Spain, Taiwan, and the Netherlands.