Increased Use of Cell Phones Not Associated With Rise in Brain Tumors

Roxanne Nelson

December 04, 2009

December 4, 2009 — It has been suggested that the use of cell phones is a risk factor for brain tumors, and the current debate over this issue has recently intensified. However, a new Scandinavian study did not find substantial changes in brain tumor incidence among adults 5 to 10 years after the use of cell phones sharply increased.

The researchers, in a report published online December 3 in the Journal of the National Cancer Institute, note that the use of cell phones sharply increased in the mid-1990s in Denmark, Finland, Norway, and Sweden. From 1974 to 2003, the incidence of brain tumors in these nations were stable, decreased, or continued a gradual increase that began before cell phones came on the market. The researchers did not detect any clear change in incidence trends from 1998 to 2003, a time period during which a possible association between cell phone use and cancer risk with an induction period of 5 to 10 years would have become evident.

"It should be noted that the population using mobile phones is very large; it is unprecedented in history that an exposure has become so prevalent in about 20 years," said lead author Isabelle Deltour, PhD, from the Institute of Cancer Epidemiology, Danish Cancer Society, in Copenhagen.

Currently, there is no clear biologic mechanism that explains how mobile phones would cause brain tumors, she told Medscape Oncology. "Experimental research has also, overall, shown evidence against a risk," she said. "But the etiology of brain tumors, in general, is poorly understood; the large majority of the cases remain unexplained, despite decades of research."

A large number of studies have investigated the relation between cell phone use and the risk of developing malignant and benign brain tumors and other types of cancers, but results from long-term studies are still limited. Study results have also not been consistent, and views among experts regarding the potential dangers of cell phone use have been conflicting.

As previously reported by Medscape Oncology, the controversy intensified in August, when a major report released by the International Electromagnetic Field Collaborative found that the regular use of cell phones can result in a "significant" risk for brain tumors.

Increased Incidence of Brain Tumors Not Seen

In the current study, Dr. Deltour and colleagues analyzed data from 1998 onward.

Cell phones were first introduced into Northern Europe in the mid-1980s, but they were not widely used until the early 1990s. Use sharply increased in the mid-1990s. Therefore, researchers contend, time trends in brain tumor incidence after 1998 are likely to be relevant to the evaluation of possible associations between brain tumors and cell phone use after 5 to 10 years of exposure.

They note that previous Scandinavian investigations found that the incidence of glioma was relatively stable from 1983 to 1998, whereas the incidence of meningioma rose between 1968 and 1997.

Dr. Deltour and colleagues analyzed the annual incidence rates of glioma and meningioma among adults between the ages of 20 and 79 years. Of a total population of 16 million adults, they identified 59,984 individuals who were diagnosed with brain tumors between 1974 and 2003.

During this time period, the incidence rate of glioma increased gradually by 0.5% per year in men (95% confidence interval [CI], 0.2% to 0.8%) and by 0.2% per year in women (95% CI, 0.1% to 0.5%). For both sexes, the incidence rate of glioma increased steadily among those 60 to 79 years of age (0.7% annual percent change for men, 0.5% for women). In other age groups, rates remained stable (ages 40 to 59 years) or declined (ages 20 to 39 years).

The authors note that they did not observe a change in the glioblastoma incidence rate trend in the overall or age-specific analyses.

When looking at meningioma, they observed that the overall incidence rate of meningioma increased by 0.8% per year (95% CI,= 0.4% to 1.3%) in men and, after the early 1990s, by 3.8% per year (95% CI, 3.2% to 4.4%) in women. The increase seen in women during this period was driven by people 60 to 79 years of age, who contributed the largest number of cases.

Overall, the authors were unable to identify any clear change in long-term time trends in the incidence of brain tumors from 1998 to 2003 in any subgroup.

Possible Reasons for Current Finding

Dr. Deltour and colleagues write that this finding could be due any number of factors: that the induction period for brain tumors associated with cell phone use exceeds 5 to 10 years; that the increased risk in this population is too small to be observed; that the increased risk is restricted to subgroups of brain tumors or cell phone users; or that there is no increased risk.

"Because of the high prevalence of cell phone exposure in this population, and worldwide, longer follow-up of time trends in brain tumor incidence rates are warranted," the authors write.

"We can only speculate what can happen in the future about a possible risk factor, [the actions of which we do not know]," she said. "Our study, which is based on very good data, allows us to exclude a risk among adults until 2003, unless it is [not] detectable in all 4 Nordic countries combined, pointing to small risks."

She also noted that, because of the uncertainties in both brain tumor etiology and the mechanisms, the length of the induction period is not known, assuming that cell phones do indeed cause brain tumors. "If mobile phones do not cause brain tumors, then 'induction period' is a meaningless concept, and we will never observe any sudden sharp increase in the incidence rates," she said.

Some case–control studies, however, have reported increased risks 5 to 10 years after the exposure that are an order of magnitude of 2. "We do not confirm these results, and if the risk was of that magnitude, we would have observed a sudden sharp increase in our study."

The study was funded by the Danish Strategic Research Council.

J Natl Cancer Inst. 2009;101:1721-1724.