Also it was unusual that the control group had zero tumors. In previous studies at the National Toxicology Program, an average of 2 percent of rats in control groups developed gliomas. Had that happened in this study, there would have been virtually no difference between the exposed rats and the controls.

“I am unable to accept the authors’ conclusions,” said one reviewer of the study, Dr. Michael S. Lauer, deputy director for extramural research at the National Institutes of Health. Dr. Lauer, whose comments were in an appendix to the report, said it was likely that the findings represented false positives.

The amounts of radiation that rats were exposed to might be higher than what cellphone users typically experience, though toxicology studies often use higher doses to make sure to detect any effect that might exist.

So we can just dismiss this study and go on using our phones?

Not totally. As the authors of the report write: “Given the extremely large number of people who use wireless communication devices, even a very small increase in the incidence of disease resulting from exposure to the RFR generated by those devices would have broad implications for public health.” RFR refers to radio-frequency radiation.

Dr. Otis Brawley, chief medical officer of the American Cancer Society, issued a statement on Friday that called this study “good science,” and called for further research because the animal research used very high signal strengths.

But he said, “The NTP report linking radiofrequency radiation (RFR) to two types of cancer marks a paradigm shift in our understanding of radiation and cancer risk.”

Dr. David O. Carpenter, director of the Institute for Health and Environment at the University at Albany, said he thought the study provided backing for the human epidemiological studies that suggested cellphone use was associated with an increased risk of gliomas and acoustic neuromas, a type of schwannoma. “I think this is real,’’ he said, suggesting people used wired earpieces to talk on cellphones.

