Some 25,000 cases of breast cancer are diagnosed each year in Britain and 180,000 in the US. Thirteen thousand British and a hundred thousand American women will die of the disease each year. In 1990, the UK government introduced a national breast screening programme, in which women aged between 50-64 are invited for a mammogram an x-ray of the breast supposedly to detect abnormalities every three years. Women over 65 will be screened on request.

The screening programme aims to catch more cancers earlier to improve the prognosis of those women affected. Some medics insist that younger women should also have the "right" to be routinely screened.

However, there is growing evidence that mammograms which, like any x-ray, involve zapping the patient with radiation can be positively harmful and even cause the disease they are intended to detect. A Canadian study, which has yet to be published in full, seems set to confirm the findings of earlier research (P Stomper and R Gelman, Hematol Oncol Clin N Am 1989; 3: 611-40) which clearly suggests that you are more likely to die from cancer if you undergo screening than if you don't. The Canadian study, using the National Breast Cancer Screening Trial, is examining the effect of mammography on women under 50. Data released so far suggests that women whose cancer was detected through mammograms have a shorter life expectancy than those who used self examination alone.

Such concerns are far from new. As long ago as the early 1980s, the late Dr Robert Mendelsohn, in Male Practice, How Doctors Manipulate Women (Contemporary Books, Chicago, 1982), wrote: "I have been warning for years that annual mammographic screening of women without symptoms may produce more cancer than it detects." Mendelsohn quoted Dr C Bailar III, editor in chief of the Journal of the National Cancer Institute, as making the same point in a 1975 report. "His conclusion was supported by numerous studies, which suggested that accumulated x-ray doses in excess of 100 rads over 10 to 15 years may induce cancer of the breast," said Mendelsohn. Dr Irwin Bross, of the Roswell Park Memorial Institute in Buffalo, New York, also warned a congressional subcommittee in 1978 that the quarter of a million women screened in the mass NCI-ACS [National Cancer Institute American Cancer Society] screening programme will "in 15 or 20 years become the victims of the worst doctor caused breast cancer epidemic in medical history."

Some women's genetic make up may make them particularly susceptible to developing cancer after exposure to "appallingly low" doses of radiation, whether from mammograms or other x-rays, according to Dr Michael Swift, chief of medical genetics at North Carolina University (New England Journal of Medicine, 27 December 1991). Around 1 per cent of women may be carrying the gene ataxia-telangiectasia (A-T) which makes them five to six times more likely to develop breast cancer and unusually sensitive to the ionizing radiation in x-rays, he says. Dr Swift studied 1,599 close relatives of people with the rare disease associated with the gene. He estimates that in the US, between 5,000 to 10,000 of the 180,000 breast cancer cases diagnosed each year could be prevented if A-T gene carriers were protected from exposure to radiation.

In reporting Dr Swift's findings, the US magazine Glamour (October 1991) cites one Scottish and two Swedish studies which found that 40 to 50 year old women who were regularly screened had either a higher incidence of breast cancer deaths than women given physical exams alone, or no significant reduction in mortality.