Cellular telephones emit and receive radiofrequency (RF) signals between about 450 and 2200 MHz which fall in the microwave region of the electromagnetic spectrum. A RF wave from a cellular telephone contains billions of times less energy than an x-ray and is not capable of inducing ionizations or damaging DNA. The rapid and widespread use of this technology, however, has raised concern over possible adverse health effects, in particular brain cancer. A few studies which addressed this concern in the United States and Sweden are non-informative, either because the follow- up was too short and numbers of cancers too small (USA) or because of serious methodological limitations (Sweden). In contrast, five well-designed epidemiologic studies have been conducted in three countries by investigators using different designs: three hospital-based case-control studies in the United States, a registry-based casecontrol study in Finland, and a registry-based cohort study of over 400,000 cellular phone users in Denmark. In our view, a consistent picture has emerged from these studies that appears to rule out, with a reasonable degree of certainty, a causal association between cellular telephones and cancer to date.
No consistent evidence was observed for increased risk of brain cancer, meningioma, acoustic neuroma, ocular melanoma, or salivary gland cancer, examined over a wide range of exposure measures, including type of phone (analogue or digital), duration of use, frequency of use, total cumulative hours of use, tumor location and laterality (concurrence of tumor location with hand normally used during phone conversations). These methodologically sound epidemiologic investigations have limitations associated with any non-experimental study, and although they are not the same across each of the studies, the influence of bias, confounding and uncertainties in exposure assessment cannot be completely discounted.
However, increased risks of 20% or higher can be excluded with a high level of confidence. Complementing the human data are the emerging results of experimental studies which have failed to confirm earlier reports of possible adverse outcomes from RF exposure. Moreover, there is no biologically plausible mechanism to support a carcinogenic effect of non-ionizing RF waves. While the current state of the science is reassuring, ongoing case-control studies being conducted in 13 countries using a shared protocol, and continued follow-up of cohorts of cellular phone users, should provide further evidence regarding any possible carcinogenic effect associated with long-term cellular telephone use.