Questions have been raised about whether cell phones might elevate cancer risks because they emit radio waves, a form of non-ionizing electromagnetic radiation.

Most studies have uncovered little or no overall increased cancer risk within the first 10 years of cell-phone use. But brain tumors can take a long time to develop. And some new research suggests that risks might increase after a decade or more of cell-phone use.

A Swedish team of scientists found that the chance of developing a malignant brain tumor doubled in some people who used cell phones for 10 or more years, according to an analysis of four case-control studies in the May 2008 issue of the International Journal of Oncology.

Longtime cell-phone users were also 2.4 times as likely to develop a benign tumor, the analysis of three other case-control studies showed. The associations were positive only for tumors on the side of the head where the phone was held.

The National Cancer Institute reports that more research is needed before drawing conclusions. Overall, studies haven't shown a consistent link or determined how cell-phone use might promote tumors and what exposure level might pose risks.

Research results are coming. A long-term study involving 13 countries is almost complete, as is the first major study of cancer risk in kids who use cell phones. Animal research has just begun.

Bottom line. The Federal Communications Commission advises that if there is any risk, and at this point we do not know that there is, it is probably very small. Until more is known, people who want to minimize potential risks of radio waves from cell phones should use the speakerphone mode or a hands-free set while on calls and ask kids to do the same. They should also limit time spent on the phone and keep the antenna away from the head and body.