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Synopsis: There has been widespread use of cellular telephones in the past decade; and a theoretical concern has been raised that this might increase the risk of brain tumors. In the past month, two reports of case control studies failed to demonstrate an increase in risk among cellular telephone users. As reassuring as these reports are, continued epidemiological vigilance is warranted.
Sources: Muscat JE, et al. JAMA 2000;284:3001-3007; Inskip PD, et al. N Engl J Med 2001;344:79-86.
The use of cellular telephones has grown remarkably in the last decade and currently there are more than 500 million subscribers to cellular-telephone services worldwide. There has been concern raised that the radiation, or even thermal effects, of cellular telephone use may confer a risk of brain cancer.1,2 Within the last two months, two substantial case-control studies were published that should allay most concerns over this question.
The first report was from five academic U.S. medical centers and published in JAMA. Between 1994-1998, Muscat and colleagues studied 469 patients with primary brain cancer between 18-80 years of age, and 422 matched controls. The main outcome examined was the risk of brain cancer in the context of hours of handheld cellular telephone use per month or years of use. The median hours of use were 2.5 for cases and 2.2 for controls. The multivariate odds ratio (OR) was 0.85 (95% confidence interval [CI] was 0.6-1.2). The OR for infrequent users (< 0.72 h/month) was 1.0 (0.5-2.0) and for frequent users (> 10.1 h/month) was 0.7 (0.3-1.4). The mean duration of use was 2.8 years for cases and 2.7 years for controls. Thus, no association was observed according to duration of use (P = 0.54).
The second report, published just two weeks later in the New England Journal of Medicine was also a case-control on patients with brain cancer seen in Phoenix, Boston, or Pittsburgh between 1994-1998. There were a total of 782 patients with brain tumors (489 with glioma, 197 with meningioma, and 96 with acoustic neuroma) and 799 controls (patients admitted to the same hospitals for a variety of nonmalignant conditions). As compared with never, or rarely having used a cellular telephone, the relative risks associated with cumulative use of a cellular telephone for more than 100 hours were 0.9 for glioma (0.5-1.6); 0.7 for meningioma (0.3-1.7); 1.4 for acoustic neuroma (0.6-3.5); and 1.0 for all types of tumors (0.6-1.5). There was no evidence that the risks were higher among persons who used cellular telephones for 60 or more minutes per day or regularly for five or more years. Tumors did not occur disproportionately often on the side of the head on which the telephone was typically used.
COMMENT by William B. Ershler, MD
Over the past several decades there has been an increase in primary brain cancers that has not been completely explained.3 A variety of explanations have been proposed, and among them is the increased use of cellular phones.3 Although of theoretical concern, there had not been any large-scale epidemiological evidence to support the notion that radiation emitted by these devices actually presented a risk for cancer. The current studies found no increased risk, and this should be a reassuring finding.
There are, however, some concerns mentioned in both articles and in the accompanying editorial.4 Most important among these is the rather long, latent period involved in brain cancer development and the rather short period of widespread use of cellular telephones. Perhaps in future decades there will be increased brain cancers recognized to be causally related to cellular telephones. Furthermore, technology is changing and there has been a shift from analogue to digital equipment. The latter actually uses and emits lower energy, and may possibly be even less of a theoretical risk. Nonetheless, cellular telephone use is becoming so prevalent that exposure is, no doubt, increasing. Thus, continued epidemiological vigilance remains important. As the old adage goes, "absence of proof is not proof of absence." In this regard, two international, multicenter investigations are just getting started. Hopefully, these will continue to demonstrate "absence of proof."
1. Maier M, et al. BMJ 2000;320:1288-1289.
2. Rothman KJ, et al. Epidemiology 1996;7:291-298.
3. DeAngelis LM. N Engl J Med 2001;344:114-123.
4. Trichopoulos D, Adami H-O. N Engl J Med 2001;