By ROBERT UHLIG
The Daily Telegraph LONDON

Radio waves from cellular phones have been found to make cancerous cells spread more aggressively - raising new concerns about the safety of using such phones.

Italian government researchers at the National Research Council in Bologna found that radio waves of the type emitted by cellphones initially killed cancer cells then, after 48 hours, made them proliferate more rapidly.

The research does not suggest that mobile phone radiation triggers cancer, but that it could play an important role hi helping cancerous cells that have already formed to thrive.

Fiorenzo Marinelli, a cell biologist, exposed leukemia cells to 900 megahertz radio waves, as used by many cellular phone networks, at a power level of one milliwatt, which is between one half and ten times the power emitted by mobile phones.

Initially, the radiation suppressed the formation of tumours. After 24 hours of continuous exposure, suicide genes that prevent cancer spreading were turned on in far more leukemia cells than in cells not exposed. But after 48 hours' exposure, Marinelli found that a survival mechanism kicked in and the cancer, briefly beaten back, became more aggressive. Three genes that trigger cells to multiply were turned on in a high proportion of the surviving cells, making them replicate ferociously, reports New Scientist magazine.

Marinelli said: "We don't know what the effects would be on healthy human cells. But in leukemia cells the response is always the same."

A British government inquiry chaired by Sir William Stewart found no evidence of any health risks from cellular phones.

However, he suggested that children, whose brains are still developing, should not use cell-phones excessively.