A high level of exposure to microwaves emitted from cell phones was associated with more than a two-fold increased risk of cancer in brain regions closest to the ear used for the phone calls, according to study authors from Sweden reporting in the May 4 edition of the online journal Medscape General Medicine. The researchers found brain tumors were most likely to develop in the temporal, temporoparietal and occipital lobes of the exposed side of the brain.

In a separate report released Thursday in London, a scientific panel commissioned by the British government to evaluate research to date on health risks of cell phones, warns that children may be at greater risk of injury from cell phone radiation because their central nervous system, including the brain, is still developing. The group, the Independent Expert Group on Mobile Phones, contends that while most studies have found few, if any, health risks from cell phones, research has also not proven conclusively that cell phones are safe, particularly for children. The group makes a number of recommendations to the British government, including the distribution to every citizen of a pamphlet outlining potential health risks of cell phones.

"Assessing the health risks of new technology is always a dilemma," says Michael Thun, M.D., vice president of epidemiology and surveillance for the American Cancer Society. "Because cellular telephone technology is new, data from large studies are not yet available on long-term use. Furthermore, the Swedish analysis is based mainly on use of analogue cell phones, which have largely been replaced by new digital phones which emit much less radiation.

"Data from small studies such as the Swedish one are often 'uninterpretable,'" Dr. Thun says. "For instance, the association between cell phone usage and brain cancer is based on only 13 brain tumor patients and is barely statistically significant."

According the study authors, "…this result was based on a low number of exposed subjects and must be interpreted with caution."

The retrospective design of the study, in which brain tumor patients and healthy subjects were asked to recall details about cell phone use and many other factors, can also introduce biases, Dr. Thun says.

"Still, one needs to be open to the possibility of a potential health threat and not require unduly high standards of evidence before taking a problem seriously," he says. "This study, however, doesn't advance our knowledge much of any relation between cell phones and brain tumors. We look forward to the results of larger studies that will become available within the next few years."

The research team, made up of Swedish physicians and scientists from the Karolinska Institute in Stockholm and the Orebro Medical Center in Orebro, was asked by the World Health Organization in 1997 to evaluate cellular telephone use and risk of brain tumors.

Study participants included 209 Swedes with malignant brain tumors, who were each "matched" for the analysis with two other healthy persons living in the same region of the country who were of the same sex and about the same age (i.e., 425 control subjects).

All participants were surveyed about past cell phone use, occupations and about other suspected risk factors for brain tumors such as use of the artificial sweetener, aspartame.

"On a broader note, the issue of discovering what factors contribute to brain cancer risk remains of critical importance," Dr. Thun says. Currently, the only environmental risk factor known to be associated with brain cancer is ionizing radiation, such as is used for diagnostic X-rays and radiation therapy. Cell phones use nonionizing microwave radiation.

The number of participants in a study is an important factor in evaluating its conclusions, Dr. Thun says. Only by including enough participants is it possible to conclude that a disease and potential risk factor are truly associated. The statistical issues are similar to observing coin tosses, he says. If you get two "heads" in a row, that doesn't mean the coin really has two heads -- a normal coin is expected to land that way 25 percent of the time.

Another issue scientists consider in evaluating results of small studies is whether any biological explanations exist for the observed association. For example, the statistical association between X-ray exposure and cancer is supported by extensive animal and human evidence that X-rays damage DNA. On the other hand, nonionizing radiation from cellular phones and other electrical products is not known to have any effect on DNA or any other cell components related to cancer. Interestingly, subjects in this study with occupations in industries (electrical, electronic or telecommunications) that might increase exposure to other sources of nonionizing radiation had no apparent increase in brain cancer risk, Dr. Thun says.

The research team has begun a much larger evaluation that includes 3,000 participants -- half with brain tumors and half without.

On a related note, Dr. Thun points out a known health concern linked to cell phone use: the four-fold risk of traffic accidents associated with speaking on a cell phone while driving a car. A report on that finding was published in the New England Journal of Medicine on Feb. 13, 1997.