Women in electrical jobs are 38 percent more likely to die of breast cancer than other working women, according to a new study that found an even higher death rate among female telephone installers, repairers and line workers.

"It's the strongest epidemiological evidence so far that breast cancer may be related to electromagnetic fields in some way, but it's still not very strong evidence," said University of North Carolina researcher Dana Loomis, chief author of the study to be published today in the Journal of the National Cancer Institute.

He and other experts said the results should be interpreted cautiously because they are based solely on listings of jobs and causes of death on death certificates for 138,831 U.S. women, including 27,814 who died of breast cancer. No measurements were taken, and the women could not be questioned about their exposure to electromagnetic fields, which are invisible pulses of radiation emitted by electric current.

However, the results do support four previous studies that found elevated breast cancer rates among male electrical workers, and are consistent with the mounting evidence that high lifetime exposure to estrogen is an important cause of breast cancer.