Medscape Medical News > Oncology
A paper published online June 22, ahead of the full report, in the Lancet Oncology summarizes the key findings from a meeting of 31 scientists organized by the IARC in Lyon, France, who considered the potential carcinogenic hazards from exposure to radiofrequency (RF) electromagnetic fields (EMFs) emitted by devices such as cell phones.
On the basis of their assessment and evaluation of the published literature, the IARC working group concluded that RF-EMFs, including those emitted by cell phones, should be considered to be "possibly carcinogenic" to humans (division 2B in the IARC classification).
The IARC working group reached their conclusion on the basis of several studies, including the results of the large INTERPHONE international case–control study and a pooled analysis of a series of Swedish studies.
Not Completely Safe
What 'possible' means is that it's not completely safe.
What "possible" means is that it's not completely safe, said working
group chair Jonathan Samet, MD. "It obviously needs to be more clearly
defined through better investigations," he explained in an interview.Dr. Samet, who is the Flora L. Thornton Chair of the Department of Preventive Medicine at the Keck School of Medicine, University of Southern California, Los Angeles, pointed out that for right now, this is a precautionary discussion.
Patients are going to be asking their physicians about cell phone safety and if there really is an associated risk for cancer. "If patients ask, the important message is that there is a possibility of risk," Dr. Samet told Medscape Medical News.
"If anyone asks what they can do to reduce the risk, it is important to emphasize that the answers are not yet in," he said. "But if they do want to do something, there are easy steps to take to lower exposure, such as using hands-free devices and reducing use of the phone."
This may be particularly important for children, who will be using these devices for a very long time, he noted. "So consideration of exposure reduction is a reasonable strategy."
Inconsistent Results
Human exposure to RF-EMF (frequency range, 30 kHz to 300 GHz) can occur from a wide range of personal devices and occupational sources. In particular, when a cell phone is held close to the ear to make a voice call, the result can be high specific RF energy absorption-rate values in the brain, note the authors.
The specific absorption rate depends on a number of factors, including the design, the position of the phone and its antenna in relation to the head, how the phone is held, the anatomy of the head, and the quality of the link between the base station and the phone.
Of particular concern is the use of these devices by children, in whom the average RF energy deposition in the brain is twice as high as in adults; in the bone marrow of the skull, it is up to 10 times as high.
The epidemiologic evidence for an association between RF-EMF and cancer is derived from cohort, case–control, and time-trend studies; wireless (cell and cordless) telephones are the most extensively studied exposure source. The conclusion that RF-EMF is possibly carcinogenic to humans was based on the results from several studies that examined the relation between cell phone use and malignant tumors.
The INTERPHONE study (Int J Epidemiol. 2010;39:675-694), a multicenter case–control study — the largest investigation of its kind to date — found that using a cell phone appeared to slightly lower the risk of developing a glioma, compared with never using one.
But when the highest 10% of cell phone users in terms of call time were analyzed, this subgroup had a 40% increased risk for glioma, compared with those who had never used a cell phone.
The results suggest that there is an increased risk for ipsilateral tumors (those on the same side of the brain as cell phone exposure) and for tumors in the temporal lobe, where RF exposure is highest.
Associations between glioma and cumulative specific energy absorbed at the tumor location were examined in the INTERPHONE study in a subset of 553 patients for whom estimated RF doses were available. For those who used a cell phone for 7 years or more before diagnosis, the odds ratio for developing a glioma rose with increasing RF exposure. Conversely, for those who used a cell phone for less than 7 years prior to diagnosis, there was no association with RF exposure.
The working group also evaluated a pooled analysis of Swedish studies (Int J Oncol. 2011;38:1465-1474), which examined the association between cell and cordless phone use and glioma, acoustic neuroma, and meningioma. For people who had used a cell phone for more than 1 year, the risk for gliomas was 1.3 times higher (30%) than that in people who had never used a cell phone.
This risk increased as time since first use increased, and with total call time. After more than 2000 hours of use, the risk was 3.2 times as high, and ipsilateral use of the cell phone was associated with more risk. Similar findings were observed for cordless phones.
The working group notes that even though the INTERPHONE study and the Swedish pooled analysis are susceptible to bias because of "recall error and selection for participation," they still conclude that the "findings could not be dismissed as reflecting bias alone, and that a causal interpretation between [cell] phone RF-EMF exposure and glioma is possible."
The INTERPHONE and the Swedish series reached somewhat different results. "The INTERPHONE study was complicated because it was a multicenter trial, and response rates weren't as good as in the Swedish studies," explained Dr. Samet. However, "the investigators did a good job of showing what biases affected their study."
Limited Evidence
Two large studies are not enough.
Dr. Samet added that there was some evidence in the INTERPHONE study
that there might be a cancer risk in longer-term users, "but it wasn't a
clear signal. The Swedish studies were clearer in that respect," he
said. "What it comes down to is that more research is needed — 2 large
studies are not enough."The working group also reviewed a Danish study that analyzed cancer rates and cell phone subscription from 1982 to 1995 and found no increased risk for glioma or other brain tumors among users (J Natl Cancer Inst. 2006;98:1707-1713). These findings were consistent with a number of earlier and smaller case–control studies. In addition, the working group examined more than 40 experimental studies.
Their conclusion was that there is "limited evidence in humans" for the carcinogenicity of RF-EMF, and a few members of the working group considered the current evidence in humans to be "inadequate." The reason for this opinion is that the results of the 2 case–control studies were inconsistent, there was no exposure-response relationship found in the INTERPHONE study, increases in rates of glioma or acoustic neuroma were not observed in the Danish cohort study, and, to date, time trends in incidence rates of glioma do not parallel temporal trends in cell phone use.
More and Better Research Needed
Not only are more studies needed, but the studies need to be better designed, explained Dr. Samet. "Doing this kind of case–control study, which relies on recall, is not the best way to go," he said. "We need prospective studies where we are actually tracking use with links to company records. We need large enough studies of that kind."
The Cohort Study on Mobile Communications (COSMOS) is attempting to do just that, he explained. It is the largest study to date, and will examine the effects of cell phone use on long-term health. COSMOS will attempt to track at least 250,000 people in 5 European countries for up to 30 years. Unlike previous studies, it will not rely on recall; instead, the study will follow cell phone use in real time.
The authors have disclosed no relevant financial relationships.
Lancet Oncol. Published online June 22, 2011. Abstract
No comments:
Post a Comment