More and more pressure is being put on women's breasts during examinations in efforts to detect smaller and smaller tumours, according to doctors from the University of Aberdeen. The amount of force used, they say, could trigger existing cancer cells to spread.
Mammography, which is used nationally to screen women aged 50 to 64 for breast cancer, involves the breast being placed in a machine and flattened between two plates so that as much tissue as possible can be X-rayed.
But in a letter in the Lancet, the medical journal, researchers from the university's Biomedical Physics department, say that tumours should always be handled gently to prevent cancer cells spreading. Experiments in animals have shown that the number of secondary tumours can increase by up to 80 per cent when a tumour is manipulated mechanically.
David Watmough, senior lecturer in the department, and Keming Quan, former research assistant, say that there has been no attempt to standardise the force used for a mammogram and that the risks have never been properly assessed.
They say that a study of breast cancer in Malmo, Sweden, found 29 per cent more deaths among women under 55 who had been screened than in women who were not.
Dr Watmough said: 'If you're spending pounds 20 to pounds 40m a year on screening women you ought to be concerned how a result like that arises.'
He said he was in favour of screening, but compression limits needed to be reviewed.