Cellular telephones, including handheld, mobile, car, and portable or bag telephones, operate on radio frequency (RF) signals in the 800- to 900-MHz range. These high frequency radio waves are similar to FM radio waves and the waves used in microwave ovens.

Allegations that handheld cellular phone use can cause brain cancer are based on the close proximity of the antenna, according to the JAMA researchers. The ear and cheek regions on the side of the head in contact with the cell phone are the areas considered to be at greatest risk of exposure to radiation from the antenna. However, the NEJM study found brain tumors did not occur more often on the side of the head on which the cell phone was usually used.

In the JAMA study, Joshua E. Muscat, MPH, of the American Health Foundation, Valhalla, New York, and colleagues studied 469 men and women aged 18 to 80 years who had primary brain cancer and compared their cellular phone use to that of 422 similar controls without brain cancer.

They found that brain cancer patients used the phones for an average of 2.5 hours a month - about the same length of time as the group without brain cancer used the phones - 2.2 hours a month.

"I see no reason at this time why people should not continue using cell phones normally," says Roy E. Shore, PhD, of the New York University department of environmental medicine, one of the study?s authors.

The study also found that patients who reported never using handheld cellular phones were actually slightly more likely to have brain cancer than were the people who used the phones. Though the average length of cell phone use in the study was almost three years, no relationship was seen between the duration of cell phone use and the likelihood of having brain cancer.

"This study points in the direction of the safety of cell phones, but additional studies are needed," Shore says. "For one thing, this is an early study -- a larger study with a number of 10-year users would be desirable."

"The existing evidence suggests that if there is a risk of brain cancer caused by cellular telephones, it is likely to be a very small risk, if it exists at all," says Michael Thun, MD, vice president of epidemiology and surveillance for the American Cancer Society (ACS). But he adds, "We can''t be 100% certain that there is no risk. The technology has not been in use long enough to be completely certain one way or the other.

"Theoretically, one would not expect this kind of radiation to pose a cancer hazard because it doesn''t damage DNA," Thun says. By the end of 1999, there were more than 86 million cellular telephone users in the U.S. "More research is in the pipeline, mostly because cell phones are most widely used," Thun says. To reduce their RF exposure, people can either use an earplug, which moves the phone away from the head, or they can use car phones that are on a speaker, he suggests.

"The greater risk from talking on a handheld cell phone is while driving," says Thun. "This has been shown to increase the risk of accidents and that is a better substantiated concern than these other remote possibilities."