The largest study to examine a potential link between cellphone use and cancer is already stirring up controversy, two days ahead of its actual release. After many years of ambiguous and sometimes conflicting results, the Interphone study was an attempt to provide a definitive measure of any risks associated with heavy cellphone use. But even the study's authors spent several years arguing over how to interpret the data that came in, before finally producing a report that's due to be published Monday evening, US time. A number of newspapers, however, have released stories on Interphone ahead of its general availability, and they suggest that the final product won't do much to clarify the health risks.

The past decade or so has seen a number of studies published that examined the potential for a link between cellphone use and cancers of tissues in the head, such as gliomas and parotid tumors. A few of these have found potential associations between heavy cellphone use and specific tumors, but these have generally used methods that are potentially subject to issues of bias—asking a user which side of the head that they typically held their cellphone on only after cancer had been spotted on one side of the head, for example. A steady flow of reports have failed to find any indication of an increased risk at all, even as cell phone use has increased dramatically.

From the biochemical perspective, there's no obvious mechanism for cellular radiation to cause genetic damage. As a result, the medical community had largely settled on the conclusion that there is no clear risk in the medium term, but longer-term (greater than a decade) risks could not be ruled out with the available evidence.

The Interphone study was an attempt to limit some of these ambiguities by recruiting a study population that was large enough to enable any signal of risk to rise above the statistical noise. Subjects were enrolled in 13 countries, and the whole effort was coordinated by the World Health Organization's International Agency for Research on Cancer. The cellphone industry provided financial support for the effort, suggesting that those with a large financial interest in its outcome would be less likely to attack any indication of risk that came out of this work.

A detailed report on the recruitment of Interphone subjects and methods used for the analysis was published back in 2007, based on progress made up through 2006. Although Interphone was based on self-reported use, the plan was to get some measure of whether the self reporting was accurate, both by obtaining records from the network providers and by installing monitoring software on participants' phones. The nature and location of cancers would be confirmed through medical records.

Despite these precautions, the authors of that paper are very much aware of the potential for bias, noting "Cases may spend time after the diagnosis of their tumour trying to understand why they have developed this disease, which might introduce a differential bias (sometimes referred to as rumination bias) in comparison with controls in recall of the amount and side of phone use."

That's where things stood in 2006; the long silence since has been filled with rumors that the authors themselves couldn't reach an agreement about how to interpret the data they had.

Apparently, the silence was due to end on Monday evening, US-Eastern time, when the study was scheduled to be published. The WHO provided advanced copies to some members of the press with the understanding that they keep from reporting on it until that time. Ivan Oransky, Executive Editor of Reuters Health, has found that this limit was widely ignored; reports started appearing as early as Saturday, leading Reuters to release its own article.

We don't have a copy of the study yet, but you can get some sense of its contents simply by scanning the headlines. For every "increased risk" and "brain cancer link," there's a headline with "inconclusive" or "no answer." At the other extreme, an industry group responded with a press release that trumpets several quotes from the paper as evidence that its products are safe. Despite its promise, Interphone has apparently left us right where we started: no obvious risk, but a potential health threat cannot be completely excluded.

Based on reading a number of the stories, it appears that, overall, cell phone use was associated with a slight protection from brain tumors—only the heaviest users saw an increased risk. Both of these effects, however, seem to have been right on the edge of statistical significance, and a number of the study's authors felt that they could probably be accounted for by the various sources of error inherent in the study design.

Perhaps more significantly, Reuters correctly points out that the study is a snapshot of the patterns of cellphone use from nearly a decade earlier now, and many things have changed significantly. Cell phone use is much, much higher, but a lot of that now involves texting or data consumption, which don't involve the user sticking the phone next to his or her head. Improved transmission protocols have ensured that the power of the signals sent by handsets has also dropped in the intervening years. All of that means that the patterns of exposure are significantly different now than they were during the period covered by the Interphone study.

We'll take a look at the study in more detail once it becomes publicly available. In the mean time, there's a reasonable chance you'll see headlines blaring about the dangers of cellphone use. All indications are that the underlying study doesn't support those conclusions—in fact, it's not clear that it supports any conclusions.