The US National Toxicology Program (NTP) will shortly release the full results of its $25m research project that involved exposing laboratory mice and rats to 10-minute bursts of cell-phone radiation for two years.

In an early release of the initial findings, the NTP researchers discovered that brain tumours had developed in the male rats, and that DNA in their brains had been damaged—something that sceptics have said was not biologically possible.

Anticipating the full results, some academics are already calling for a reclassification of mobile phone radiation as a definite carcinogen (cancer-causing agent) in humans. Dr Anthony B Miller, a professor at the Dalla Lana School of Public Health at the University of Toronto, stated at a lecture last month: "The evidence indicating wireless is carcinogenic has increased and can no longer be ignored."

Dr Miller was part of the working group created by the World Health Organization that, in 2011, classified mobile phone radiation as a group 2B carcinogen, which means it is possibly harmful to humans.

But he says that, based on new evidence from the NTP and others, the classification should be stronger, and reflect the true harm that the radiation can cause.

The early findings of the NTP study, which was initiated by the US's Food and Drug Administration (FDA), had a mixed reception. The American Cancer Society altered its advice about mobile phone use and urged people to limit the time the phones are held to the head, but others—including groups funded by the mobile phone industry—were sceptical. They pointed out that brain cancer rates haven't increased in the years mobile phones have been used, but that is true only for brain tumours in general, while rates of GBMs have risen.