The National Toxicology Program (NTP), a division of the National Institutes of Health (NIH), has found a link between the type of radiation emitted by cell phones and cancer in rats. The project has been underway for more than a decade, and with a $25 million price tag, is the most expensive ever undertaken by the program.

The study involved more than 2,500 rodents, exposed to the same type of radiation found in cell phones, at the same frequencies, for nine hours everyday, for two years.

The findings—that male rodents experienced low incidences of two types of tumors—seem to support earlier findings from epidemiological studies, which found the same types of tumors in humans, and which led the International Agency for Research on Cancer to classify radiation as a possible human carcinogen, back in 2011. The tumors found were gliomas (in the brain), and schwannomas (of the heart).