The high rate of breast cancer in the US is caused by liberal use of medical x-rays, a leading expert has claimed.

Many women were given high doses of x-rays by doctors before the carcinogenic effects of radiation were appreciated. Probably 75 per cent of all the 182,000 cases of breast cancer reported in the US every year are due to medical x-rays, he says.

The claims are made by John Gofman, professor of molecular and cell biology at the University of California, after he studied medical research going as far back as 1910.

But Gofman's conclusion has not impressed many cancer experts, who fear that many women may be frightened off from having mammograms, which supposedly detect early cancers.

Since preparing his book, Preventing Breast Cancer, Gofman has increased his estimates of cancers caused by x-rays to 90 per cent.

He points out that x-ray therapy was once very prevalent, used to to treat a range of conditions from pneumonia to acne and hair removal. Gofman estimates that women's breasts receive 0.4 rad of medical x-rays a year for each year of life; then, comparing that dosage with the levels suffered by Japanese atomic bomb survivors, he reckoned that 114,000 women, or 62 per cent of those diagnosed every year with breast cancer, could blame x-rays as the cause. But, he added, as he had built in so many caveats, he increased the figure to 75 per cent to give a fairer indication.

(Preventing Breast Cancer, by Dr John Gofman, published by the Committee for Nuclear Responsibility, Inc., San Francisco, California).

A recent study doesn't go along with Gofman's findings. The National Cancer Institute has assessed the breast cancer risk among radiologic technicians, and found that their work was not a contributory factor (JAMA, August 2, 1995).