Purpose: This literature review investigated the possible association between the use of mobile phones and brain tumors.
Methods: In brief, 11 publications were retrieved from JSTOR, PubMed, Google Scholar, and Summon in order to compare the association between the usage of mobile phones in patients with a brain tumor and those without. Papers published in English, and after 2001 were selected for. There was no limit on age, gender, geographical location and type of brain tumor.
Results: For regular mobile phone usage, the combined odds ratios (OR) (95% confidence intervals) for three studies was: 1.5 (1.2-1.8); 1.3 (0.95-1.9); and 1.1 (0.8-1.4), respectively. Furthermore, the odds ratio did not increase, regardless of mobile phone use duration. Additionally, Lonn et al (2005) observed that the risk also did not significantly increase when assessing the laterality (ipsilateral or contralateral) of the tumor in relation to side of head used for the mobile phone. Kan et al (2008) observed an OR of 1.22 when comparing analog phone to digital phone use.
Conclusion: This review concluded that there is no current association between mobile phone use and the development of brain tumors. Although certain studies speak in favor of an increased risk, many are plagued with either: sampling bias, misclassification bias, or issues concerning risk estimates. Further research needs to be done in order to evaluate the long-term effect of mobile phone usage on the risk of developing a brain tumor.
In the past 20 years, the use of cellular telephones has increased exponentially in today’s society, with greater than 5.3 billion mobile subscriptions worldwide (Cardis, 2011). Consequently, numerous concerns have been raised regarding the connection between radiofrequency signals emitted from these devices and the possible risk of developing chronic diseases. Although current guidelines state that mobile phones emit energy levels far too low to cause any deleterious health effects, there has been growing debate as to whether a relative risk has not been established due to the different levels of exposure when the research was initially conducted. Especially since early mobile phones were developed with an analog technology, and emitted radiofrequency waves of only 800-900 megahertz (Mhz) (Linet, 2013) and recent years have seen it become replaced with a digital technology which utilizes much higher radiofrequencies (ranging up to 2200 Mhz) (Linet, 2013)
As such, numerous attempts have been made to evaluate this connection based on the standard of mobile phone usage today – with much of the research focusing on the effects of mobile phone usage and the development of tumors, particularly in the head and neck region. In particular, research has focused on tumors particular to the temporal area of the brain – a region proposed to experience the most exposure to mobile phone radiation – including tumors like, meningiomas, gliomas, and acoustic neuromas (Christensen, 2003). The current argument in favor of an association proposes that although low frequency radiation is non-ionizing - in that it does not damage DNA - if presented at high enough levels the radiofrequency radiation can induce a thermal change in tissues and thereby stimulate tumor growth (Linet, 2013).
Yet despite this growing database of scientific research, the topic still remains controversial. While some case-control studies have purported to find a connection between brain tumors and increased mobile phone usage via a tumor “promoter” effect (Hardell, 2003), other case-control studies find no short-term effects of cell phone electromagnetic field exposure on brain pathology (Mandala, 2014). At present, any evidence arguing for a causal relationship between mobile phone use and the development of brain tumors has been found to be inconclusive upon further critical examination (Kundi 2009).
In this study, we compared the observed patterns for brain tumor incidence trends in a variety of publications, particularly those of a meta-analysis or case control nature, in order to investigate the association between mobile phone use and the risk of brain tumor development.
Incidence data was gathered from a variety of databases including: JSTOR, Pub med database (http://www.ncbi.nlm.nih.gov/pubmed), Google Scholar (http://www.scholar.google.com) and Summon. The keywords specified to search for the articles include: Cellular phone, Cancer, Tumor, Brain, Mobile phone, Short term, Long term, Cross-sectional, Meta-analysis, Radiofrequencies, Glioma, Meningioma, and Schwannoma. In order to ensure the information presented is valid and applicable to the topic, all of the articles chosen will be published between 2001 and 2014. Additionally, due to the lack of consensus on research areas on this topic, the study populations selected will include both male and female cellular phone users of any age group, in any geographic setting. Lastly, in order to avoid any misunderstandings in discourse, only papers published in English will be selected for. Non-human studies were discarded.
To assess for a possible causal relationship between mobile phone use and cancer, all of the data gathered from the publications and analyzed in order to construct an evidence table based on the findings of each study. Those studies demonstrating the relationship between mobile phone use and brain tumor development were assessed by their subgroups in order to gather information based on tumor histology, tumor location (ipsilateral or contralateral), type of phone (analog or digital), and amount of use. If there are no valid counter arguments against a particular piece of evidence for an association then causation is suggested. However, when the evidence is insufficient the confidence in a causal relationship decreases.
In brief, 14 articles were selected for this review paper. Five of those articles were a level 4, six articles were level 3, and two were level 1. One of the level 3 studies focused on brain cancer incidence trends in the United States, specifically in its Caucasian population (2010). Similarly, Benson et al (2013) examined the incidence of intracranial tumors in middle-aged women in the United Kingdom. Additionally, while Cardis et al (2011) conducted a case-control study solely on patients with newly diagnosed acoustic neuromas in 13 countries using a common protocol; Schuz et al (2011) used two Danish nationwide cohort studies to assess acoustic neuroma occurrence. Another the level 4 articles was centered on cell phone use and the implications to brain tumor risk in adolescents with a mean age of 12.3 years (Aydin, 2011). The remaining publications selected assessed the risk of any intracranial tumor with increased mobile phone usage, regardless of gender, age, or race. As such, the chosen articles were also targeted to allow for direct comparisons, with respect of mobile phone usage, and its subsequent radiation exposure, to the development of brain tumors in individuals in the control group who were found to be without a brain tumor.
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Table 1: Summary of study designs reviewed
The articles analyzed focused on a variety of factors for their assessment of causality. Two articles measured the duration of cell phone usage and cancer incidence rate. Five out of eleven articles addressed tumor location (ipsilateral or contralateral) compared to patient mobile phone. Four out of eleven articles evaluated the risk of developing more than one type brain tumor with mobile phone use. Three out of eleven articles compared the cancer incidence risk between analogy and digital phones. Further detail on the articles can be found in the evidence table (See Appendix A, Table A.1).
Lahkola et al (2006) examined the effect of mobile phone use on a risk of developing a variety of intracranial tumors by conducting a meta-analysis involving 12 studies (Figure 1). The odds ratio (OR) was found to be insignificant at 0.98 (95% confidence interval; CI = 0.83-1.16) for all intracranial tumors related to mobile phone use. For gliomas, the pooled OR was 0.96 (95% CI 0.78-1.18), for meningiomas it was 0.87 (95% CI 0.72-1.05), and for acoustic neuromas it was 1.07 (95% CI 0.89-1.30). Kan et al (2008) conducted a similar study examining the OR for high-grade gliomas, meningiomas, and acoustic neuromas. The pooled OR was valued at being lower than 1, and the odds ratio for low-grade glioma was found to be insignificant with a OR = 1.14 (95% confidence interval; CI = 0.91 to 1.43] (Kan, 2008).
Similarly, Johansen et al (2001) analyzed various intracranial and body tumors and their association with mobile phone use (Figure 1). The standard incidence ratio (SIR) for brain tumors was 0.86 (95% confidence interval; CI = 0.83 to 0.90) in males, therefore showing no evidence of an increased risk for tumors of the brain.
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Figure 1: Pooled odds ratio of original studies and meta-analysis of mobile phone use and intracranial tumors. Studies including gliomas (1), meningiomas (2), acoustic neuromas (3).
When measuring brain tumor incidence risk based on location relative to cell phone placement, Larjavaara et al (2010) found that on a case analysis basis, tumors were found to be located contralateral to cell phone placement, but not in a manner that was statistically significant. The odds ratio for this brain tumor risk among contralateral regular phone users (at least 1 call per week for a period of 6 months or more) was higher than the OR of ipsilateral regular phone users OR = 0.87 and OR = 0.82, (95% CI), respectively. Additionally, it was concluded that although nearly 97% to 99% of the energy from a mobile phone is absorbed by the hemisphere within 5 cm of the handset, there was no excess of gliomas found in the temporal lobe among regular users compared to the never regular users (28% vs. 33% of the locations in the cerebral lobes) (Larjavaara 2010).
Christensen et al (2003) also did not detect an increase in frequency on a particular side of the head relative mobile phone placement, nor did they find that tumor size correlated with the pattern of cell phone usage (Table 2).