Concern has risen about the connection between brain tumors and heavy use of cellular telephones among the estimated 90 million U.S. persons who use these devices. Recent medical investigations have not substantiated an increased risk. The National Cancer Institute sponsored a large, sophisticated study of this matter, and Inskip and colleagues reported the results of this retrospective case-control study.

Information from 782 brain tumor cases was collected from three hospitals across the country over a four-year period from June 1994 to August 1998. These cases were compared to 799 control patients admitted to the same hospitals for other reasons. Of the eligible cases identified, 92 percent agreed to participate, and 80 percent successfully completed the interviews.

In the study, cumulative use of cellular telephones for 100 hours or more did not appear to impart any greater risk for brain tumor development than no use of cellular telephones (relative risk for brain tumor: 1.0). Curiously, subjects who reported using cellular telephones for 500 hours or more were found to be 30 percent less likely to develop brain tumors (relative risk: 0.7) than persons who did not use cellular telephones. Relative risks for subtypes of brain tumors (gliomas, meningiomas and acoustic neuromas) were also near 1.0 relative risk, implying no apparent association between cellular telephone use and various subtypes of brain tumors.

The authors concluded that no apparent association exists between cellular telephone use and brain tumors. These results were put into context by the authors in their discussion f the various limitations of the study, including its retrospective design and the recall bias inherently possible in a case-control study. Small differences in relative risk could not be ruled out, according to Inskip and colleagues. In addition, the authors discussed the possibility of a long latency period between cellular telephone use and subsequent brain tumor development that would not be identified by this study because cellular telephone use became widespread only in the past decade.