New Delhi Feb 14: At a time when various studies are going on whether radiation from mobile phones is harmful for health an US expert Saturday said no study or research has proved that non-ionizing radiation as produced by these devices causes cancer. No study or research about cancer has proved that non-ionizing radiation causes cancer. There is a campaign doing the rounds that the use of mobile phones or the proximity to mobile phone towers can cause cancer. Proponents of the theory question arguments in favour of the safety of mobiles. How can you be so sure about it