The Cell Phone-Cancer Enigma: Do We Have Reason To Worry?
Alan BC Dang
January 21, 2006 3:08 AM
comment(s) - last by
Recent study claims no evidence of a link between cellphone use and cancer but results were contradictory, leading in both directions
British Medical Journal
published a paper evaluating the relationship between mobile phone use and gliomas, a type of a cancer that represents 50% of all primary brain tumors. The researchers found no evidence to support the claim that cell phone use increases the likelihood of being diagnosed with a glioma. Unfortunately this doesn't mean that we know cell phones are safe.
In this case-control study, the researchers interviewed 966 patients who had been diagnosed with a glioma in the UK. These patients were asked to recall the frequency and duration of their calls, the side of their head that the phone was used on, whether or not they used hands-free ear pieces, as well as the specific types of phones that were used. The researchers then obtained the same information from 1,716 individuals who did not have cancer. When the two groups were compared, no evidence was found to suggest that there was an increased risk of glioma compared to the cumulative number of calls and hours of use.
The researchers did however encounter interesting findings. There was evidence suggesting that there was a higher risk of developing a tumor on the same side of the brain where the phone was used. Their 95% confidence interval was 1.02 to 1.52, meaning that there was somewhere between 2 to 52% increase in risk for developing a tumor and that there was only a 5% chance that the difference could be less than 2% or higher than 52%. In parallel to this finding, they found a reduced risk of tumor when the phone was used on the opposite side of the head. This time, the range was a 7 to 39% reduction in risk with only a 5% chance that the reduction in risk was less than 7% or greater than 39%.
Despite their conclusion about having no evidence, this bit of data actually supports the claim that cell phones can be dangerous. However, the researchers write that these differences are due to recall bias because patients know the side of their brain that has cancer. Patients may be biased into reporting that they used the cell phone more frequently on the cancerous side.
This inadequate evidence for either conclusion captures the problem of a case-control study: recall bias. If you cannot trust your subjects to accurately remember which side of their heads they use their phones on more frequently, how can you trust the rest of the data? Other problems with the study were that the researchers were only able to interview 51% of the patients who they identified as having gliomas "mainly because rapid death prevented [the researchers] from approaching all of them." Finally, the researchers only looked at one type of brain tumor and not others.
In the end, the study does not give any definitive results. It simply says that evidence could not be found on whether or not cellphones were dangerous. In addition, there
statistical evidence suggesting that tumors were more likely to be seen on the same side a phone was used, although there are confounding variables that may come into play.
While a cohort study (where people are followed over time) would be better than the case-control study (where people are asked to look back in time), the nature of medical research involves doing lower-budget research first before moving on. These types of studies open the door for more expensive and bigger studies. Bottom line? More research is needed before we really know the answer.
More information on gliomas
can be found here
Hepworth SJ, et. al.
Mobile phone use and risk of glioma in adults: case-control study. BMJ, doi:10.1136/bmj.38720.687975.55 (published 20 January 2006)
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Disagree with comments
1/21/2006 3:52:14 PM
"Despite their conclusion about having no evidence, this bit of data actually supports the claim that cell phones can be dangerous. However, the researchers write that these differences are due to recall bias because patients know the side of their brain that has cancer. Patients may be biased into reporting that they used the cell phone more frequently on the cancerous side."
I think this is poor reasoning. If the study finds no increase in total cases, but there is a reported increase in cases for people who have cancer on the side of their head they used the phone on (and a potentially very large one at that!), then there are two possible conclusions:
1) The effect is real, but canceled out by a second effect that somehow prevents or cures brain cancer on the other side of the head so that the totals balance out.
2) People with brain cancer are more likely to report favoring the side of the head they got cancer in because they're heard speculation from their doctors and the media about cell phones.
I don't think cell phones can cure or prevent cancer, so I tend to accept #2.
"This inadequate evidence for either conclusion captures the problem of a case-control study: recall bias. If you cannot trust your subjects to accurately remember which side of their heads they use their phones on more frequently, how can you trust the rest of the data? "
The most important data here is mortality and caner rates. These have nothing to do with patient's recall: its quite clear when someone has died, so I don't think trust is an issue here. We definately no when a patient dies, and assuming they did autopsys, we should be sure they died of a brain tumor too.
"Other problems with the study were that the researchers were only able to interview 51% of the patients who they identified as having gliomas "mainly because rapid death prevented [the researchers] from approaching all of them."
51% is actually not a bad number for a study like this. Not enough to be concerned about anyway.
Anyway, the important thing to take away here is that there was no evidence for the effect. That means if it does exist, its a very subtle effect, and very likely only affects a tiny minority of people. Research will likely go on for some time before it can be proven to not exist (or to be too subtle to pick up from this study), but in either case, the most interesting outcome (a strong effect), appears to have been more or less ruled out.
RE: Disagree with comments
1/21/2006 4:27:02 PM
You bring up good points, but the third option is that the statistics and limitations of a case-control study can produce an artifact. You can't say either way.
"The most important data here is mortality and cancer rates."
Those are the effects. The question is of the exposure. Hours of cell phone use were obtained by patient recall as opposed to looking at the cell phone records. Usually peple over report rather than under-report cell phone use, but what about frequency of using the hands-free earpiece.
"Anyway, the important thing to take away here is that there was no evidence for the effect. That means if it does exist, its a very subtle effect, and very likely only affects a tiny minority of people."
Exactly. But even if there was only a 1% chance, if you're in that 1% group, you have cancer. Fundamentally people are biased toward zero risk.
"The most interesting outcome (a strong effect), appears to have been more or less ruled out."
Yes, for gliomas. The other concern is a glioma simply a cancer in glial cells. Cancer means that that the cells grow inappropriately. You may be able to induce inappropriate growth through several different oncogenes or other causes, and you cannot rule out the possibility that the patients who died happened to have cell-phone induced cancers, and that cell-phone induced cancers happen to be a specific type of high-grade glioma that's different. The WHO grading of gliomas is histologic, meaning it's based upon how things look on a microscope.
It think it was a great study, but it has the limitations inherent to a case-control study, and it's not the "definitive answer" that it's being made to be. Researchers in the field aren't about to pack up and call it a done deal.
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