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Higher Glioma Risk Not Seen
for Regular Cell Phone Users
Smart Safe Hollow Air Tube
Home Protection Detector
Cell Phone Radiation Protection
Roxanne Nelson
March 08, 2012
March 21, 2012 — The controversy surrounding the health
risks related to cell phones continues to evolve.
A new study, published online March 8 in BMJ, suggests that
there is little evidence linking cell phone use to a higher
risk for glioma. The researchers note that the higher risks
seen previously are not consistent with the incidence trends
they found in the American population.
"Our study looked at actual rates of glioma in the United
States, in comparison to projected or expected rates of
glioma based on observations from the INTERPHONE study [Int
J Epidemiol. 2010;39:675-694] and a study in Sweden [Int J
Oncol. 2011;38:1465-1474]," explained lead author Mark
Little, DPhil, senior scientist at the National Cancer
Institute (NCI) in Rockville, Maryland. "We found that
actual glioma rates declined over the study period."
The researchers used population-based data from 1992 to
2008, reported in 12 Surveillance, Epidemiology, and End
Results (SEER) registries, to determine glioma incidence.
When they modeled the incidence rates projected in the
INTERPHONE study, which showed slight increases in glioma
risk among a small number of heavy users, they found that
they were not statistically distinguishable from the actual
rates in the United States.
However, "when we modeled incidence rates projected from the
Swedish study, we found that the actual rates would need to
be at least 40% higher than what was observed," he told
Medscape Medical News. "Thus, actual glioma rates in the
United States are consistent with the INTERPHONE study, but
not with the rates based on the Swedish study."
Usage Increased, Rates Generally Did Not
From 1992 to 2008, the age-specific incidence rates of
glioma remained generally constant (a 0.02% decrease per
year), while cell phone usage increased substantially in the
American population (from about 0% to almost 100%).
"In general, the study suggests that there is not a large
excess risk for glioma associated with cell phone use," said
Dr. Little. "However, it cannot rule out a modest excess
risk for a small number of heavy users."
"In that sense, the study is broadly reassuring," he added.
"However, we recommend continued surveillance of glioma
rates for a number of reasons, including changing usage
patterns and technology, and because tumor latency may be
longer than has been observed to date."
Evidence Inconsistent
The link between cell phone use and brain and central
nervous system tumors has been widely investigated, but
results have been inconsistent. Some studies have not
supported the association, whereas others have observed
modest to large increases in relative risk, usually of
glioma. There have also been some reports of an increased
risk for acoustic neuroma.
Last year, the International Agency for Research on Cancer
heated up the controversy over cell phone safety when it
classified radiofrequency electromagnetic fields as possibly
carcinogenic to humans, as reported by Medscape Medical
News.
Some of the strongest evidence supporting an association
between brain tumors and cell phone use comes from a series
of studies led by Lennart Hardell, MD, PhD, from the
Department of Oncology, Orebro Medical Center, Sweden (Int J
Oncol. 2006;28:509-518; Int Arch Occup Environ Health.
2006;79:630-639; Arch Environ Health. 2004;59:132-137;
Pathophysiology. 2009;16:113-122). These studies showed that
risk increased with the number of cumulative hours of use,
higher radiated power, and length of cell phone use. They
also reported that younger users were at higher risk.
A Rising Trend?
Approached for independent comment, Dariusz Leszczynski,
PhD, DSc, pointed out that the NCI study does not show that
cell phone radiation causes brain cancer, but it does show
that brain cancer in the United States is slowly rising.
"This study does not give a precise reason for this trend,"
said Dr. Leszczynski, a research professor at the Radiation
and Nuclear Safety Authority in Helsinki, Finland.
"Because trends are based on real data, not just assumptions
or predictions [as were used in INTERPHONE and the Swedish
studies], we can believe that there is a slow increase in
brain cancer in the United States," he explained. "What is
important is that for the first time, scientists admit that
[this increase]...might be caused by cell phone
radiation-induced brain cancer — assuming that this
radiation causes brain cancer."
Dr. Leszczynski noted that the conclusions from the NCI
study open the door for more speculation, but emphasized
that epidemiology or trend data will not give us the
much-needed answer. "We need to show in molecular-level
studies that cell phone radiation activates processes in the
human body that lead to the development of brain cancer," he
said. "We don't have such studies yet."
Currently, only 3 molecular-level studies of cell phone
radiation have been conducted in humans — one from Dr.
Leszczynski's lab. "We do not know if this radiation has an
effect on human physiology and, if it has, what kind of
impact it has," Dr. Leszczynski explained.
Study Details
In the NCI study, Dr. Little and colleagues estimated
projected rates of glioma by combining the relative risks
that were reported in the INTERPHONE and the Swedish study,
and adjusted them for age, registry, and sex. They analyzed
data for 27,457 cases of glioma, and concentrated on 24,813
cases in adults.
Although glioma rates were generally stable during the study
period, low-grade gliomas and those with a poorly specified
anatomical location decreased 3.02% and 2.35% per year,
respectively. There was also a modest increase in rates of
gliomas of the temporal lobe and other specified sites
during the study period (0.73% and 0.79% per year,
respectively).
The researchers point out that there is no evidence of the
20% decrease in glioma risk (that is, a relative risk of
0.8) seen for regular cell phones users in the INTERPHONE
study.
Based on relative risks from the Swedish study, predicted
rates of glioma were much higher than, and therefore
statistically inconsistent with, observed rates, the authors
conclude. "However, based on relative risks from the
INTERPHONE study, projected rates could be consistent with
the observed data."
The study was funded by the Intramural Research Program of
the National Institutes of Health, and the Division of
Cancer Epidemiology and Genetics at the National Cancer
Institute. The authors have disclosed no relevant financial
relationships.
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