Those who are worried about the possible health risks of cellphones just received some backing from a significant source: the World Health Organization. A group within the organization, the International Agency for Research on Cancer, has announced it is listing the electromagnetic radiation produced by cell phones as "possibly carcinogenic." The IARC's use of the term "possibly" is key to the decision, as its expert panel determined that the information available is too limited to say anything with a greater degree of certainty, but is sufficient to warrant careful monitoring.

The designation is the result of a meeting held last week that brought 31 health researchers together to evaluate the conclusions that can be drawn from current research, including unpublished information from the Interphone study. The conclusions will eventually appear in The Lancet Oncology, but the IARC has issued a press release ahead of publication.

As we recently discussed, the wavelengths used for cellular communications are only known to influence human tissue via heating, and the researchers involved with the designation do not propose anything new here. The panel also recognizes that most of the epidemiological research involving human exposure to radio frequencies is ambiguous; for all but two types of cancer, the current state of information is officially deemed "inadequate."

For those two types of cancer, glioma and acoustic neuroma, the committee considered the evidence to be somewhat stronger, rising to the level of "limited." According to the IARC, this means that "A positive association has been observed between exposure to the agent and cancer," but "chance, bias or confounding could not be ruled out with reasonable confidence." One of the members of the group, USC's Jonathan Samet, said that this designation means that "There could be some risk, and therefore we need to keep a close watch for a link between cell phones and cancer risk."

For these types of tumor, there is some evidence that those users who self-report as being among the heaviest cell phone users have a higher rate of incidence at longer time points. However, there's no clear trend in risks with increasing use, and self-reported behavior can often be unreliable, hence the caution expressed by the report and its authors.

So if everyone involved is being cautious about our limited state of knowledge, why the worrisome designation? Officially, the IARC places cell phones in Category 2B of their classification of cancer risks, and that's a pretty broad category:

This category is used for agents for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals. In some instances, an agent for which there is inadequate evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals together with supporting evidence from mechanistic and other relevant data may be placed in this group. An agent may be classified in this category solely on the basis of strong evidence

from mechanistic and other relevant data.

All indications are that cell phones fall into the first of these categories: limited evidence of risk in humans, and nothing significant from laboratory animals. Samet's suggestion—that we need to keep a close watch in the form of further studies—makes a great deal of sense but is probably superfluous; there's no doubt those studies are in progress.

Even if our knowledge hasn't changed, the fact that the World Health Organization has weighed is sure to shift the debate. Although few people are likely to end up reading The Lancet Oncology in order to get a firm grasp on the limitations of our current knowledge, the mere use of the term "carcinogen" will probably have a potent effect on both the public's imagination and the ability of legislators to enact limits on the exposure to wireless radiation.