An anonymous reader quotes a report from NBC News: A giant U.S. study meant to help decide whether cellphones cause cancer is coming back with confusing results. A report on the study, conducted in rats and mice, is not finished yet. But advocates pushing for more research got wind of the partial findings and the U.S. National Toxicology Program has released them early. They suggest that male rats exposed to constant, heavy doses of certain types of cellphone radiation develop brain and heart tumors. But female rats didn't, and even the rats that developed tumors lived longer than rats not exposed to the radiation. The National Toxicology Program, part of the National Institutes of Health, is still analyzing the findings. But John Bucher, associate director of the program, said the initial findings were so significant that the agency decided to release them. A 29-year-old study published earlier this month from Australia reassures us that cellphones are reasonably safe, and do not cause cancer.