In male rats, the studies linked tumors in the heart to high exposure to radiation from the phones. But that problem did not occur in female rats, or any mice.

The rodents in the studies were exposed to radiation nine hours a day for two years, more than people experience even with a lot of cellphone use, so the results cannot be applied directly to humans, said John Bucher, a senior scientist at the National Toxicology Program, during a telephone news briefing.

Continue reading the main story
The results, he said, had not led him to change his own cellphone use or to urge his own family to do so. But he also noted that the heart tumors in rats — called malignant schwannomas — are similar to acoustic neuromas, a benign tumor in people involving the nerve that connects the ear to the brain, which some studies have linked to cellphone use.