Cancer is one of the most common causes of disease and death worldwide (WHO 2009, Fact Sheet 297). 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.
The carcinogenic effects of ionizing radiation such as UV, X-rays and gamma radiation in the upper range of the electromagnetic spectrum were investigated and verified in experimental and epidemiological studies. Based on the evidence of these findings, the International Agency for Research on Cancer (IARC) classified ionizing radiation as "carcinogenic to humans" (Group 1).
In the lower range of the electromagnetic spectrum, an increased incidence of childhood leukemia in the vicinity to 50/60 Hz magnetic fields of power transmission lines was observed by Wertheimer and Leeper 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 contradictory 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 µT. In 1999 the IARC classified extremely low frequency magnetic fields as a "possible human carcinogen" (Group 2B) in the same group as caffeine although there was no known biological mechanism despite intensive laboratory research. In contrast to ionizing radiation, the amount of energy produced by electromagnetic fields is too weak to directly change or break chemical bonds through ionization.
Thus, potential effects of electromagnetic fields on biological systems have to be mediated by other mechanisms. 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 mobile phones, i.e. electromagnetic waves in the middle range of the electromagnetic spectrum (radio frequency) on cancer initiation.
The development of cancer is a complex process that depends on several factors and the mechanisms that lead to cancer are only partially understood yet. According to the classical three step model of carcinogenesis with initiation, promotion and tumor progression of cancer the process starts with an initial altered cell and lasts years up to decades until a tumor develops. Newer models often assume more complex multi-stage processes that can include up to ten different mutations, depending on tumor type.
Medical and biological studies with experimental designs, known from other disciplines such as toxicology, are necessary to provide evidence for basic effects. These studies include in vitro investigations of blood samples, cell cultures or isolated DNA as well as animal experiments. With their standardized laboratory test environment and large sample sizes (animals, cells) they fullfill the required preconditions for statistical data analyses to evaluate potential effects on cancer. Compared to epidemiological studies, potential risks can be identified after a relatively short period of time. In ideal case, if an effect is found, experimental studies can lead to elucidate the underlying mechanism of action.
In contrast, epidemiological studies examine a potential relationship between mobile phone use and tumor incidence in different groups of the population. Due to the long lasting process of carcinogenesis results are often available only after several years or decades (see epidemiological studies).
With in vitro studies also genotoxic effects of electromagnetic fields can be investigated, such as chromosome aberrations, sister chromatid exchange, formation of micronuclei, DNA stability or DNA strand break, or effects on cell proliferation or apoptosis (see genotoxicity). However, such studies only help to understand the inital stages of carcinogenesis or isolated processes which can be examined on a single cell model. Substances that are tested positive in genotoxic studies are not necessarily carcinogenic. Moreover, results from in vitro studies cannot be transferred onto complex organisms without limitations.
Epidemiological studies as well as experimental studies on genotoxicity, cell proliferation or apoptosis are not considered for the present evaluation. Nevertheless, for a general evaluation of the subject "cancer and mobile phones" they should be involved.
The present summary is based on animal studies (mostly rats or mice) that investigated the origin of tumors and tumor growth parameters under exposure to mobile phone-related frequencies. A problem of studies on mobile phone-related frequencies and cancer development is that researchers oftentimes want to explore athermal effects of electromagnetic fields separately from thermal effects. This requires very low exposure doses which limits the possibility of finding strong effects. Especially for detecting effects of rare events extensive sample sizes are necessary to achieve statistical significance. To avoid this problem animal strains (e.g. Eµ-Pim or AKR/J-mice) with increased susceptibility to tumor formation (due to their genetic constitution) are used to improve the detection of an additional increase in tumor frequency.
Due to great heterogeneity between the animal studies (see table) it is difficult to evaluate the health effects of mobile phone-related frequencies on the initiation of cancer. The studies differ with respect to their frequency range (800 to 1.966 GHz), the different types of modulation (TDMA, CDMA, FDMA, etc.), SAR values (0.0077 to 4.2 W/kg), exposure duration (<10 days up to two years) as well as the investigated cancer types, the used animal strains und the used examination methods (palpation, histopathological analysis of isolated organs/all organs). Some studies expose animals in the near field, others use far field exposure. Because often only one group is tested with one exposure strength, a dose-response relationship is difficult to analyse. A dosimetric problem of several studies is that changes in growth and body weight of the tested animals during the course of the experiment cause differences in SAR values that are oftentimes not considered. As a consequence the reported SAR values of some studies might be unrealistic. Other problems arise from small sample sizes with their associated statistical uncertainty or from limited analyses of sentinel animals to evaluate the general health status of the study population.
From 33 available studies in the EMF-Portal (november 2010), ten studies investigated general cancer initiation in different organs, nine studies focused on brain tumors, tumors of the spinal cord and the central nervous system, five studies examined lymphoma development, four studies analysed the development of mammary tumors, three studies investigated skin tumors and two studies focused on liver cancer.
30 out of 33 studies did not find effects of mobile phone-related electromagnetic fields on cancer initiation, cocarcinogenesis or tumor promotion. Tillmann et al. (2010) found a cocarcinogenic effect of lifelong UMTS exposure in female mice offspring whose dams had been exposed to electromagnetic fields and were simultaneously co-exposed to the carcinogen ethylnitrosourea. Anghileri et al. (2005) observed that in exposed animals compared to control mice, carcinogenesis may be induced earlier and with different pathological forms. According to the results of Repacholi et al. (1997) lymphoma risk was found to be significantly higher in the exposed mice than in the controls. However, the study was critized due to several limitations, such as variations of SAR values, investigation of only one single exposure group, lacking evaluation of predeceased animals and missing replacement of deceased animals (which is relevant for homogeneity of the electromagnetic field). Moreover, two later studies with a similar experimental design did not confirm the results of Repacholi et al.: Utteridge et al. (2002) and Oberto et al. (2007) investigated the same mouse strain (Eµ-Pim1) and did not find an influence of longterm GSM exposure on lymphoma incidence.
Within the fifth framework program of the European Union (FP5), the funded project PERFORM-A (In vivo Research on Possible Health Effects of the Use of Mobile Telephones and Base Stations (Carcinogenicity Studies in Rats and Mice) adressed the research question whether radiofrequency electromagnetic fields in animal species like mouse or rat have carcinogenic or cocarcinogenic effects. To avoid problems known from earlier studies an effort was made to ensure consistent experimental conditions: three exposure groups were tested in a standardized and accredited laboratory setting (good laboratory praxis [GLP]). All experiments were blind studies and the highest exposure doses were below limit values known to produce thermal effects. Further, a uniform tumor terminology according to IARC/WHO standards was used. The project consisted of four subprojects with different experimental settings. Three out of four studies did not find evidence that exposure to mobile phone-related frequencies had adverse effects or an influence on incidence, severity or latency of any neoplastic or non-neoplastic condition. The only effect observed was a borderline one in the subproject PERFORM-A3 investigating the DMBA- induced mammary tumor response.
The following researchers compiled results from several scientific studies in extensive overviews of the literature, so called reviews, to evaluate the potential effects of mobile phone-related electromagnetic fields on cancer development:
At the international level, the WHO is the responsible institution for statements on the effects of electromagnetic fields. In a recent Factsheet (Nr. 193) from 2010 the WHO draws the following conclusion on the results of animal studies: "Results of animal studies consistently show no increased cancer risk for long-term exposure to radiofrequency fields."
At the national German level, the Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS) is the responsible authority. In 2008, the BfS issued a report on the studies of the German Mobile Telecommunication Research Programme, which also included the topic cancer: "Taken together, in the analysed studies no differences between the experimental groups were found that would indicate an influence of chronic whole body exposure (GSM-900 or UMTS with SAR 0.4 W/kg) on tumor development." In the final conclusion of the report is stated: "The experimental studies of the German Mobile Telecommunication Research Programme [...] do not indicate a health relevant effect of radiofrequency electromagnetic fields below the limit values on cancer development of the haematopoietic system [...]."