The director of a leading US cancer research institute has sent a memo to thousands of staff warning of possible higher risks from mobile phone use. Ronald Herberman, of the University of Pittsburgh Cancer Institute, said users should not wait for definitive studies on the risk and should take action now. He said children should use mobiles in emergencies only and adults should try to keep the phone away from the head. No major academic study has confirmed a link to higher brain-tumour risks. Dr Herberman said his warning was based on early findings from unpublished data. "We shouldn't wait for a definitive study to come out, but err on the side of being safe rather than sorry later," he says. "I am convinced that there are sufficient data to warrant issuing an advisory to share some precautionary advice on cell phone use," the memo says.