Study: No Link Between Brain Tumors, Cell Phones; Expert: But…
by Roxanne Nelson, BSN, RN, medscape.com, 12 May 2016
A large study has found no link between cell-phone use and brain tumors, although this is undoubtedly not the last word on the controversial subject.
In fact, according to one expert, the analysis lumped together all brain cancers and did not separate out high-grade gliomas (especially in the temporal or frontal lobe), which are the most relevant type.
In their study, the researchers examined age- and sex-specific incidence rates in 19,858 men and 14,222 women diagnosed with brain cancer in Australia from 1982 to 2012.
The findings show that the incidence of brain cancer did not increase during the study period in any group except those 70 to 84 years of age.
But in this group, the incidence of brain cancer began to increase in 1982, before the introduction of cell phones.
Over the past 2 decades, the use of cell phones has increased dramatically, from about 9% in 1993 to about 90% currently. However, age-adjusted incidence rates for brain cancer in those 20 to 84 years of age have risen only slightly in men over the past 30 years (P < .05), and have remained stable in women (P > .05).
Overall, no increase in the incidence of brain cancer can be considered compatible with the steep increase in cell-phone use.
The study was published online May 5 in Cancer Epidemiology.
The findings from this study confirm those from studies published in the New Zealand, the Nordic countries, the United Kingdom, and the United States, all of which were unable to prove the hypothesis that "mobile phones cause brain cancer," said lead researcher Simon Chapman, AO, PhD, emeritus professor in public health at the University of Sydney in Australia.
"The radiation from cell phones is nonionizing, so it is highly unlikely to cause cancer," he toldMedscape Medical News.
The incidence of brain cancer is also higher in men than in women, and sex differences have been observed in other cancer types. But "there is no evidence that men use phones more often or longer than women," Dr Chapman pointed out.
The slight increase observed in men is explained by the higher incidence in the oldest age group. "There is no rise across time in any younger age groups, and there is a much higher incidence in the oldest age groups — age being the biggest predictor of most cancers," he explained.
"The rise brain cancers in the oldest age group preceded the introduction of phones so can't be explained by mobile phone use," Dr Chapman added.
Controversy Put to Rest?
Previous studies on the link between cell phones and cancer have been a mixed bag, ignited controversy, and come to various conclusions.
Approximately 30 epidemiologic studies have attempted to evaluate the association between cell-phone use and the risk for brain and salivary gland tumors, as reported by Medscape Medical News. There have also been a number of experimental studies involving cell cultures and animal models.
Although some studies have shown an increase in the risk for brain cancers, others have found no association.
But for at least one expert, the controversy has been put to rest.
"For most of us, the issue of brain cancer and cell phones is resolved," said John D. Boice Jr, ScD, president of the National Council on Radiation Protection and Measurements. "There is no risk. There is no biological mechanism and no animal study or cellular study that finds reproducible evidence of an effect."
The Australian study is interesting, but there are many descriptive studies that also show no change in brain tumor incidence over time, Dr Boice, who is a professor of medicine at the Vanderbilt University School of Medicine in Nashville, Tennessee, told Medscape Medical News.
"The best epidemiologic studies are two prospective studies that are convincingly negative," he said. "The weak evidence from case–control studies are plagued with low response, differential response between cases and controls, and response bias."
However, another expert who has extensively researched the link between cell phones and brain cancer does not feel that these results are conclusive.
"We have consistently found an increased risk for high-grade glioma, including the most malignant type, glioblastoma multiforme grade IV, and use of wireless phones," said Lennart Hardell, MD, PhD, from the Department of Oncology at University Hospital in Örebro, Sweden.
"Moreover, the risk is highest for tumors in the frontal and temporal lobes — areas with highest exposure to radiofrequency radiation during use of the handheld phone," he told Medscape Medical News.
"The study by Dr Chapman and colleagues does not give incidence data for high-grade glioma located in the temporal or frontal lobe, so I am afraid that their study is not very informative," Dr Hardell pointed out. "Lumping together all types of brain tumors, regardless of location in the brain, hampers any conclusions on incidence trends."
He also noted that the real increase in the use of cell phones occurred recently, with the introduction of smartphones.
Increase Only in Oldest Adults
In their study, Dr Chapman and his colleagues modeled expected rates by age group (20–39, 40–59, 60–69, 70–84 years) using data from published studies, which reported relative risks of 1.5 in ever-users of cell phones and of 2.5 in people deemed to be "heavy users" (19% of all users).
A 10-year lag period was assumed between the start of cell-phone use and evidence of an increase in the number of brain cancer cases.
Overall, the incidence of brain cancer was higher in men than in women (8.7 vs 5.8 per 100,000). However, the researchers calculated that the expected incidence rates in 2012 should have been 11.7 per 100,000 (P < .01) in men and 7.7 per 100,000 (P < .01) in women.
In 2012, only 1434 cases of brain cancer were observed, whereas 1867 cases were expected.
In all age groups, expected incidence rates were higher than observed rates.
The most likely explanation for the rise in adults older than 70 years is improved diagnosis, Dr Chapman and his colleagues point out. In Australia, CT and related imaging technologies were introduced in the early 1980s.
Dr Boice agrees. "CT scans and brain imaging did improve detection," he said.
"The increase among the elderly in Australia, though, is likely also related to stereotactic brain biopsy, where tissue can be obtained relatively easily and diagnoses greatly improved," Dr Boice explained. "In the past, cutting the brain of elderly patients was not likely, so a specific diagnosis of brain tumor not made."
The authors have disclosed no relevant financial relationships.
Cancer Epidemiol. Published online May 5, 2016. Abstract