A recent meta-analysis and a conference have renewed attention to the question of whether cellular telephone use increases brain-tumor incidence.
“Cell phones are now used worldwide by more than 3 billion people, and there is increasing heavy use by children,” says Michael J. Thun, MD, MS, American Cancer Society vice president emeritus of epidemiology and surveillance research.
According to Thun, approximately 30 epidemiological studies have looked at the possible relation between cellular telephones and benign and malignant brain tumors as well as acoustic neuroma and salivary-gland tumors. Although most studies found no significant associations, some did. Nearly all available evidence is from case-control studies with less than 20 years of follow-up since the introduction of cellular telephones, and these studies have some methodological limitations. “The 2 greatest limitations are that the information about cell-phone use is obtained retrospectively from people who have already been diagnosed with cancer and that participation in the studies has been considerably lower among controls than cases. Uncertainties about the evidence can only be resolved by longer-term epidemiologic follow-up and by critical evaluation of experimental studies that report biological effects from cell phones,” said Thun.
While epidemiologists continue to collect new data and reanalyze available data, individuals and policymakers struggle with the need to base today's decisions on what is known today.
Meta-analysis is a valuable statistical tool for combining results from multiple studies, but the conclusions are subject to the same methodologic limitations as the studies themselves and can be influenced by assumptions and choices in the way data are collected and analyzed. Among the 4 meta-analyses in the published literature as of October, 2009, 3 found no significant association.
The most recent meta-analysis was conducted by researchers from several South Korean institutions, including the National Cancer Center in Goyang, the Ewha Womans University in Seoul, and the National University Hospital in Seoul, and from the University of California, Berkeley. The results were published in the Journal of Clinical Oncology (epub ahead of print on October 13, 2009; DOI: 10.1200/JCO.2008.21.6366). Lead author, Seung-Kwon Myung, MD, MS, and colleagues reported no overall association for the combined results of 23 relevant studies, but they found a statistically significant 9% increased risk when the meta-analysis was limited to the 10 studies the authors classified as low bias, and a significant 15% lower risk for data from the remaining studies labeled as high bias.
In interpreting these findings, Thun notes that it is important to remember that this meta-analysis was limited to case-control studies. The largest study of cellular telephones and cancer risk published so far is a cohort study, a design less prone to the biases that plague case-control studies but also with shorter follow-up than the later case-control studies. That cohort study found no excess cancer risk among cell-phone users. All of the studies in which researchers who interviewed subjects were “blinded” to their status as cases or controls are from a single research group in Sweden. These studies collectively show a statistically significant 17% excess brain tumor risk. The remaining 15 studies found a nonsignificant 2% reduction in risk.
Another key issue is whether the researchers' criteria for high-quality studies and their emphasis on blinded interviewers were appropriate.
Thun also says some important studies have not yet been published, such as the combined results from Interphone, a large study of cell-phone use and brain tumors being done in 13 countries under the supervision of the International Agency for Research on Cancer (IARC, a part of the World Health Organization). According to a May 2009 note on the IARC website (http://www.iarc.fr/en/media-centre/iarcnews/2009/interphone_status.php), the results have already been submitted to a journal and should soon be available. This study has been criticized because the results reportedly show that cell-phone use is associated with lower, not higher, brain cancer risk, and because it was funded by the telecommunications industry. However, the greater use of cellular telephones among controls than cases probably reflects the lower participation rate among controls than cases (and a greater probability that controls who used cellular telephones would participate in the study). Although the study received funding from the telecommunication industry, oversight of the study was conducted by a committee of scientific experts who were independent of the industry.
A September 2009 meeting in Washington, DC, sponsored by the National Institute of Environmental Health Sciences, University of Pittsburgh, Environmental Health Trust (an organization devoted to researching environmental health risks) and several other organizations coincided with a Senate hearing on the topic, as well as a recent report on cell-phone safety by the Environmental Working Group. According to the report, concerns about cell-phone radiation exposure have prompted several countries, including Germany, Switzerland, Israel, United Kingdom, France, and Finland, to recommend limiting exposure to it, especially for children. This action was based on the Precautionary Principle and the widespread use of cellular telephones, rather than on scientific certainty. The report asks why the United States hasn't taken similar action.
One concern about cellular telephones is that the induction period for many carcinogens is long and that adverse effects on cancer may appear only after decades of follow-up. This does not explain why case-control studies in Sweden are reporting increased risk after 10–15 years of use. Another concern is that children may be more susceptible than adults. Current epidemiological data cannot dismiss these concerns, because of limited follow-up, especially for children. On the other hand, cellular telephones do not produce ionizing radiation, and the reports of other biological effects of cellular telephones that could effect carcinogenesis have yet to be replicated.
There is, as yet, no regulatory tradition in the United States to require product changes or recommend consumer behaviors based on weak scientific evidence. However, those who are concerned about exposure to electromagnetic fields from cellular telephones can virtually eliminate their exposure by using devices that place the telephone antenna further from their head and can limit use of cellular telephones by their children. 1