When the media fixates on a medical topic, doctors know that a flurry of patient questions will inevitably follow. So it helps to be prepared with responses to hot-button questions, such as those surrounding the recent resurgence of the potential link between cell phones and brain cancer. Inspired by the World Health Organization moving the radiofrequency magnetic fields produced by cell phones to the classification of “possibly” causing cancer in late May, some newspapers handled the topic with subtle headlines like IS YOUR CELL PHONE KILLING YOU?. Though the fevered media response of some outlets was countered by thoughtful explainers from other sources, many physicians will surely still face questions from patients on the topic. But how does a busy doctor brush up on the extensive literature testing the link between cell phones and cancer?
A: You attend a literature review talk, such as the one given by hematology/oncology fellow Daniel Geynisman at Monday’s installment of the department’s weekly seminar. In half an hour, Geynisman sped through the most important studies examining cell phones and brain cancer, drawing out the important results, criticisms, and implications of the experiments. The primary message was simple – there’s no need to panic, or to go back to using exclusively landlines and pagers. But a true danger does exist with cell phones, Geynisman said, one that’s worth sending a warning to patients – and doctors themselves.
The lingering mystery around cell phones and cancer is caused by an epidemiological quirk, Geynisman explained. Proving the link between a rare exposure and a rare cancer – such as asbestos and mesothelioma – is relatively straightforward. Finding a link between a common exposure and a common cancer is more difficult, but can be done, as it was with smoking and lung cancer. But conclusively proving the connection between a common exposure, such as cell phones, with a rare cancer, such as glioma or acoustic neuroma, is much more difficult. Only about 10,000 new cases of glioma are diagnosed each year in the United States, while more than 300 million cell phones are currently in use in the country. To prove that the use of phones significantly increases brain cancer rates, enormous numbers of subjects would have to be collected and followed.
Those challenges have forced most researchers into a flawed study design, Geynisman said. Retrospective case control studies are commonly used in epidemiology, but are subject to an important confounding factor called recall bias. If you ask 3,000 people with brain tumors and 3,000 controls about their history of cell phone use, those with cancer are more likely to remember and report unusually high amounts of use. In one study, subjects were found to over-estimate their cell phone use by almost three times, adding a hefty dose of salt to any case control results.
Despite this issue, early case control studies found a relative risk of 1, indicating no increased or decreased risk for brain tumors in users of cell phones. But the question did not go away, fueled by the research of a Swedish group who dialed the data down to find increased risk among very specific groups: people who used cell phones for more than 10 years, or people who started using the phones before the age of 20. The INTERPHONE study, which surveyed over 6,000 people with brain tumors and 7,000 controls from 13 countries, might have settled the dispute but for one result. Published last year, most of the risks calculated for various groups and tumors showed a negative association with cell phone use, suggesting (improbably) that talking on the phone protected against brain cancer. But one association still stuck out – heavy cell phone users showed a 40 percent increase in the risk of glioma. Statistical anomaly, or cause for concern?
The result was apparently enough for the WHO to place cell phone radiation in the same group as other potentially carcinogenic compounds ranging from lead and coffee, and for more studies to be conducted, Geynisman said. After all, ubiquitous cell phone use is a relatively recent development, so more time may need to pass before the health effects can be accurately assessed. A prospective study, called COSMOS, will tackle some of these questions, as it follows a quarter-million subjects for at least 25 years and measures cell phone use as it happens, instead of through memory. But while scientists, physicians, reporters, and the general public wait for those results, they can caution the world about the real dangers of cell phones, which have nothing to do with cancer.
“What’s not shaky is that cell phone users are four times more likely to be distracted drivers and texting poses a risk of 23 times more collisions. 81 percent of Americans use their cell phones while driving, and almost a third of crashes involve cell phones,” Geynisman said. “So you can keep using your cell phone probably, but don’t do it while driving.”