Study Finds No Cell Phone-Brain Cancer Link
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For those who remain unconvinced, a team of Danish researchers reported that long-term data do not support a link between use of mobile phones and risk of brain cancer. During an additional five years of follow-up, there was no association between central nervous system tumors and subscription to a mobile phone service, Patrizia Frei, PhD, of the Danish Cancer Society, and colleagues reported online in BMJ. "In general, our findings are in line with most of the epidemiological research that has been conducted to date," Frei told MedPage Today. "They are also in line with in vitro and [animal] studies that show no carcinogenic effects on the cellular level." Nor were there any associations when assessed by length of subscription or tumor type, they reported. "I'm impressed with the quality and size [of the study], so I think it significantly weakens the idea that cell phones can cause brain cancer," Timothy Jorgensen, MD, of Georgetown Lombardi Comprehensive Cancer Center, told MedPage Today and ABC News. Several epidemiological studies have turned up no increased risks of brain cancer with mobile phone use. The largest of these, the INTERPHONE study, found no risk of glioma or meningioma in general with use of the devices, although it did find a greater risk of glioma in those with the greatest levels of use. However, those levels were criticized as "implausible" -- a word many used to describe the study overall, given findings in the same study that cell phone use appeared to be protective against cancer in certain groups. And last spring, a work group of the WHO declared the radiofrequency electromagnetic fields emitted by cell phones to be "possibly carcinogenic to humans" -- a mild category that includes progestins and anti-epileptic drugs. Still, epidemiologists say the weight of the evidence has shown that cell phone chatting doesn't cause cancer. Earlier results from the Danish study found no evidence of an increased risk of brain or nervous system tumors or any cancer among cell phone users. In their updated report, Frei and colleagues looked at data on 358,403 subscribers followed through 2007 who had accrued 3.8 million person-years of usage. During that time, there were 10,729 cases of tumors of the central nervous system. Overall, the researchers found that there was no risk of brain or central nervous system tumors for men or women. When assessed by the longest length of use -- 13 years of subscription or more -- there was no significant association with tumors (incidence rate ratio 1.03 for men, 0.91 for women). Nor did those who'd been subscribed for 10 or more years have an increased risk of meningioma or glioma, they reported, noting that these data clarify earlier findings showing a diminished risk for this group. However, those results were based on only 28 cases and the researchers suspected they were due to chance, Frei said. When she and colleagues looked at the data by tumor subtype, they found a slight but nonsignificant increased incidence rate ratio for glioma in men -- though there was no relationship with this type of cancer for women, they found. Men also had a 22% reduced risk of meningioma, but there was no association for women, they added, although the numbers were small. They added that further subdivision of gliomas in men by site showed a marginally increased risk for cancer in the temporal lobe, but it wasn't significant -- an "important" finding given that the temporal lobe "has been described as the region of the brain with the highest absorption of energy emitted from mobile phones." The study was limited by a potential misclassification of exposure, as those who have a subscription but do not use it may be misclassified. Nor did the researchers have information on actual phone usage, so they couldn't determine the risk of the subgroup of heaviest users. Still, researchers pointed out that using subscription plan data had a number of advantages. "They assumed that people who subscribe to cell phone plans are using their phones, and I think that's a reasonable assumption," Jorgensen said. "The alternative is to talk to people and ask them to tell you about their cell phone use. But people are notoriously inaccurate." In an accompanying editorial, Anders Ahlbom, PhD, and Maria Feychting, MD, PhD, of the Karolinska Institute in Stockholm, said not relying on self-report is certainly an advantage of the study. Yet they cautioned that "having a mobile phone subscription is not equivalent to using a mobile phone, and conversely some users will be nonsubscribers." Still, they said the findings are in line with numerous other epidemiological studies that have found no increased risk of brain cancer with cell phone use. "The research that has been conducted for the safety of public health with regard to this new and rapidly spreading technology is now extensive," Ahlbom and Feychting wrote. "The question is how much more research is needed." "Continued monitoring of health registers and prospective cohorts is warranted," they wrote, "but more case-control or other studies with built-in selection and recall bias are not needed." The study was supported by the Danish Strategic Research Council and by grants from the Swiss National Science Foundation. Neither the researchers nor the editorialists reported any conflicts of interest. This article was developed in collaboration with ABC News.  | ||
| Primary source: BMJ Source reference: Frei P, et al "Use of mobile phones and risk of brain tumors: update of Danish cohort study" BMJ 2011; DOI: 10.1136/bmj.d6387. Additional source: BMJ Source reference: Ahlbom A, Feychting M "Mobile telephones and brain tumors" BMJ 2011; DOI: 10.1136/bmj.d6387. |
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