PITTSBURGH — The head of a prominent cancer research institute issued an unprecedented warning to his faculty and staff Wednesday: Limit cell phone 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 tumors and cell phone 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Herberman is basing his alarm on early, unpublished data.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 says 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 cell phone users and especially parents.

In the memo he sent to about 3,000 faculty and staff Wednesday, he says children should use cell phones 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 says. He even warns against using cell phones 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 tumor patients and concludes "we found no overall increased risk of brain tumors among cellular phone users. The potential elevated risk of brain tumors 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 Web site.

Still, Herberman cites a "growing body of literature linking long-term cell phone 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 cell phone use," he wrote in his memo.

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