A new in-depth peer reviewed study conducted by the US government has found a link between mobile phone usage and cancer.

On 26 May, the National Toxicology Program released its partial findings on rodent toxicology and carcinogenesis studies of radio frequency radiation after the results were earlier reported by Microwave News website. According to the report, over two thousand rats which were exposed to radiation from mobile phones showed "low incidences" of two types of tumours in both the brain and the heart.

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Rats that were not exposed to the frequencies had no cases of tumours.

"Given the widespread global usage of mobile communications among users of all ages, even a very small increase in the incidence of disease resulting from exposure to [radio-frequency radiation] could have broad implications for public health," according to partial findings of the $25m study.

The cancerous tumours were found only in male rats and similar symptoms were not present in females. Rats that were exposed to radio-frequency energy in utero tended to have slightly lower birth weights.

"Where people were saying there's no risk, I think this ends that kind of statement," said Ron Melnick, who ran the NTP project until retiring in 2009 and recently reviewed the study's results.

Scientific American spoke to biochemist and director of the Science/Health Science Learning Center at the University of Colorado, Jerry Phillips about the results and how to reconcile mobile phone usage with the potential health hazards.

"I'll connect the phone to Bluetooth in my car. Or I'll text. Or I if I have to make a phone call I put it on speaker," he explained. "But you have to realize that this issue opens up a much bigger can of worms than cell phones.

"If this radiation, this form of energy can interact with biological tissue then it's going to reopen a lot of what were supposedly settled issues regarding the safety of wireless communications. If we're going to be bathed in a whole new electromagnetic environment, how safe is it?"

Both sides of the mobile phone debate have over the years been proving their standpoints. In early May a survey of brain cancer rates in Australia showed no increase after the introduction of cell phones.

NTP has, however, acknowledged that the research is not definitive and that a deeper study is required. Complete results of the report will be released by end-2017.