A Conversation with Dr. Martha Linet about Cell Phone Use and Cancer Risk
The International Agency for Research on Cancer (IARC) published a synopsis of its Monograph on the Evaluation of Carcinogenic Risks to Humans June 22 in The Lancet Oncology. The monograph classifies exposure to mobile phones as "possibly carcinogenic to humans." Dr. Martha Linet, chief of the Radiation Epidemiology Branch in NCI's Division of Cancer Epidemiology and Genetics, discusses the IARC working group's decision and summarizes some of the ongoing research on mobile phones and cancer risk.
Is there evidence of an increased risk of cancer from mobile phone use?
Most studies to date have not found an association between cell phone use overall and the development of tumors. However, there are a handful of studies that have shown an association with increased risk for glioma among the small number of cell phone users who reported the highest level of call time. Among the positive studies, results are conflicting and don't show a dose-response. In addition, there is no biologically plausible mechanism or animal evidence for how cell phones might cause cancer.
Why are there inconsistencies among the studies?
Most of the studies are based on data from interviews about cell phone use patterns from brain tumor patients and control subjects. We know that this kind of self-reported data is not necessarily accurate. Patients may be more likely to over-report use than controls, or they may mis-recall on which side of their head they held their phone. Cell phone technology has changed dramatically over time, and the studies cover different periods. The way people use cell phones has also changed over time, which makes accurate recall more difficult.
In addition, none of the epidemiologic studies measure actual radiofrequency exposure to the brain; the exposure is estimated from interview data.
How has the epidemiology community responded to IARC's decision to classify mobile phones as "possibly carcinogenic to humans?"
There's been a lot of lively debate among epidemiologists and interest at epidemiologic meetings. We have identified some gaps in the research, which ongoing studies are attempting to address. The three major gaps are: none of the studies—including Interphone, a large international study on cell phone use of more than 5,000 patients in 13 countries who had either glioma or meningioma—have a large number of long-duration, heavy-intensity cell phone users. So, risks associated with high exposures are based on fairly small numbers.
Second, there are no published studies of cancer risk among people who began using phones as children or adolescents.
Third, the animal studies have been limited to date, but the National Toxicology Program has a very large, well controlled study of rodents under way, involving thousands of rodents. Results are expected in 2014.
Would you describe some of these forthcoming studies?
There is a large European study, involving mostly Nordic and northern European countries, called COSMOS, that is following 250,000 people 30 to 59 years of age with repeated interviews, comparisons with cell phone subscriber data, and periodic linkage with cancer registry data.
There are several NCI-funded studies in the United States looking at cell phone and radiofrequency exposure and risk of meningioma and other brain tumors in different populations. (See the sidebar for more information.)
And there is another European-funded initiative called Mobi-Kids that is modeled after Interphone. Mobi-Kids is studying brain tumor risk associated with cell phone use among people 10 to 24 years of age.
What is the main takeaway from all of this?
The IARC working group classified cell phone use as a possible carcinogen. If one keeps in mind that possible means "maybe," that fits with the positive reports but overall inconsistent data. The studies under way addressing key research gaps will provide important information that should clarify questions not addressed by the research to date, and it will be important to continue to monitor incidence trends in brain tumors.
The steps suggested by the Food and Drug Administration and the Federal Communications Commission to reduce exposure include reducing the length and number of calls made from cell phones, using landline phones instead of cell phones, and switching to a cell phone with a hands-free device.
Of course, one of the most important general safety recommendations is to not use cell phones while driving.
The Epidemiology and Genomics Research Program in NCI's Division of Cancer Control and Population Sciences is funding four population-based case-control studies of meningioma. Investigators are collecting information on potential risk factors, including cell phone use, from individuals diagnosed with intracranial meningioma and comparing them with control subjects matched by sex, ethnicity, geographic location, and age. These studies represent the first concentrated effort to examine environmental and genetic risk factors for meningioma.