A newly released study from the National Toxicology Program, a division of the National Institutes of Health, has found a link between the kind of radiation emitted by cell phones and cancer in rats.

This study has been a long time in the making, note our esteemed colleagues over at Consumer Reports — and it’s cost the government a pretty penny, at a cost of $25 million. It’s the most expensive ever undertaken by NTP, involving more than 2,500 rodents.

Those rats were exposed to the same kind of radiation cell phones emit for nine hours a day, every day, over a period of two years. Researchers found that male rodents experienced low incidences of two type of tumors: gliomas, in the brain, and schwannomas, in the heart. It’s unclear if female rats experienced the same issue or were part of the the study.

Consumer Reports notes that these results seem to support earlier findings from epidemiological studies, which found the same kinds of tumors in humans. That led the International Agency for Research on Cancer to classify radiation as a possible human carcinogen in 2011.

So what do these results mean? On the one side, there are industry leaders and others who say that evidence has shown cell phones don’t pose any risks to human health.

But then there are scientists and some health officials who argue that more research needs to be done but point to available evidence as enough to suggest that there’s a possible connection between cell phone use and brain cancer. That’s enough to justify taking precautions when you’re yapping away with your phone up to your ear, some say.

“This study in mice and rats is under review by additional experts,” a spokesman for the NIH said in a statement to Consumer Reports. “It is important to note that previous human, observational data collected in earlier, large-scale population-based studies have found limited evidence of an increased risk for developing cancer from cell phone use.”

For now, there will definitely be increased debate between the two sides on what exactly this study means for the average person, and whether or not something should be done as a result. The NTP’s site says the results could be used by the Food and Drug Administration and the Federal Trade Commission in determining the best way to protect consumers from the potential harms of radiation that comes from cell phones.

The cell phone industry is likely to push back, as wireless trade group CTIA has said in the past that cell phones are totally safe. It’s been on the front lines pushing back on laws in cities like Berkeley, CA and San Francisco that would require retailers to notify consumers about the potential risks of using cell phones.

The Federal Communications Commission weighed in on the study’s results today, saying in a statement:

“We are aware that the National Toxicology Program is studying this important issue. Scientific evidence always informs FCC rules on this matter. We will continue to follow all recommendations from federal health and safety experts including whether the FCC should modify its current policies and RF exposure limits.”

Cell Phone Radiation Causes Cancer in Rats, Government Study Finds [Consumer Reports]