The head of a prominent cancer research institute issued an unprecedented warning to his faculty and staff Wednesday: Limit cellphone use because of the possible risk of cancer.

The warning from Dr. Ronald B. Herberman, director of the University of Pittsburgh Cancer Institute, is contrary to numerous studies that don't find a link between increased tumours and cellphone use, and a public lack of worry by the U.S. Food and Drug Administration.

Herberman is basing his alarm on early, unpublished data. He said it takes too long to get answers from science and he believes people should take action now — especially when it comes to children.

"Really at the heart of my concern is that we shouldn't wait for a definitive study to come out, but err on the side of being safe rather than sorry later," Herberman said.

Herberman's advice is sure to raise concern among many cellphone users and especially parents. In the memo he sent to about 3,000 faculty and staff Wednesday, he said children should use cellphones only for emergencies because their brains are still developing.

Adults should keep the phone away from the head and use the speakerphone or a wireless headset, he said. He even warns against using cellphones in public places like a bus because it exposes others to the phone's electromagnetic fields.

The issue that concerns some scientists — though nowhere near a consensus — is electromagnetic radiation, especially its possible effects on children. It is not a major topic in conferences of brain specialists.

A 2008 University of Utah analysis looked at nine studies — including some Herberman cites — with thousands of brain tumour patients and concludes "we found no overall increased risk of brain tumours among cellular phone users. The potential elevated risk of brain tumours after long-term cellular phone use awaits confirmation by future studies."

Studies last year in France and Norway concluded the same thing.

"If there is a risk from these products — and at this point we do not know that there is — it is probably very small," the Food and Drug Administration says on an agency website.

Still, Herberman cites a "growing body of literature linking long-term cellphone use to possible adverse health effects including cancer."

"Although the evidence is still controversial, I am convinced that there are sufficient data to warrant issuing an advisory to share some precautionary advice on cellphone use," he wrote in his memo.

Do you want to play Russian roulette?

A driving force behind the memo was Devra Lee Davis, the director of the university's centre for environmental oncology.

"The question is do you want to play Russian roulette with your brain," she said in an interview that she did from her cellphone. "I don't know that cellphones are dangerous. But I don't know that they are safe."

Of concern are the still unknown effects of more than a decade of cellphone use, with some studies raising alarms, said Davis, a former health adviser in the Clinton administration.

She said 20 different groups have endorsed the advice the Pittsburgh cancer institute gave, and authorities in England, France and India have cautioned children's use of cellphones.

Herberman and Davis point to a massive ongoing research project known as Interphone, involving scientists in 13 nations, mostly in Europe. Results already published in peer-reviewed journals from this project aren't so alarming, but Herberman is citing work not yet published.

The published research focuses on more than 5,000 cases of brain tumours. The National Academy of Sciences in the U.S., which isn't participating in the Interphone project, reported in January that the brain tumour research had "selection bias." That means it relied on people with cancer to remember how often they used cellphones. It is not considered the most accurate research approach.

The largest published study, which appeared in the Journal of the National Cancer Institute in 2006, tracked 420,000 Danish cellphone users, including thousands that had used the phones for more than 10 years. It found no increased risk of cancer among those using cellphones.

A French study based on Interphone research and published in 2007 concluded that regular cellphone users had "no significant increased risk" for three major types of brain tumours. It did note, however, that there was "the possibility of an increased risk among the heaviest users" for one type of brain tumour, but that needs to be verified in future research.

Earlier research also has found no connection.

Cellphones emit radiofrequency energy, a type of radiation that is a form of electromagnetic radiation, according to the National Cancer Institute. Though studies are being done to see if there is a link between it and tumours of the brain and central nervous system, there is no definitive link between the two, the institute says on its website.

"By all means, if a person feels compelled that they should take precautions in reducing the amount of electromagnetic radio waves through their bodies, by all means they should do so," said Dan Catena, a spokesman for the American Cancer Society. "But at the same time, we have to remember there's no conclusive evidence that links cellphones to cancer, whether it's brain tumours or other forms of cancer."