A FRESH controversy has arisen about mammograms. Radiobiologists in Germany say the millions of women who are genetically predisposed to breast cancer should avoid mammogram screening. But other experts reject the claim that the X-rays in mammograms greatly increase the risk.
鈥淲omen with an inherited, increased breast cancer risk should avoid frequent and early mammography screening,鈥� warns Marlis Frankenberg-Schwager of the University of G枚ttingen. Instead they should insist on other methods of screening, such as magnetic resonance imaging, she says.
As many as 1 in 200 women inherit mutations in the BRCA1 or BRCA2 genes, greatly increasing the risk of breast cancer. At the moment, doctors encourage them to have annual mammogram check-ups from as early as age 25.
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But research by Frankenberg-Schwager鈥檚 team suggests that the low-energy X-rays used in mammograms are nearly three times as effective at mutating genes in human cells as conventional X-rays (International Journal of Radiation Biology, vol 87, p 781). A typical 4-milligray mammogram could damage the genes in 16 out of every 100 million cells, she says.
Most women have two healthy copies of each BRCA gene, so the chances of both being knocked out in the same cell are remote. But for women with inherited mutations, whose cells have only one healthy copy of a BRCA gene, the chances are much greater. 鈥淚t is a big risk for these women,鈥� Frankenberg-Schwager says. 鈥淚t is worrying.鈥�
Britain鈥檚 National Radiological Protection Board rejects her warning, though. 鈥淚 don鈥檛 see good cause for reconsidering mammography screening,鈥� says Roger Cox, the board鈥檚 head of radiation effects. He points out that the International Commission on Radiological Protection in Stockholm estimated that the additional risk from mammograms to women with BRCA mutations was just a fraction of 1 per cent.
But Dieter Frankenburg, a co-author of the paper, says this applies only to women over 40 and doesn鈥檛 take into account the greater mutational effect of low-energy X-rays. By combining evidence from the victims of Hiroshima and Nagasaki with the team鈥檚 findings on mammogram X-rays, he calculates that any women under 20 who have 10 mammograms of 4 milligrays increase their chance of breast cancer by a factor of 2.5. There are no figures specifically for women under 20 with BRCA mutations, or those aged between 20 and 40, but Frankenburg鈥檚 team believe the risk is far greater than a fraction of a per cent.
Richard Kennedy of Queens University in Belfast agrees that X-rays are risky for young women with BRCA mutations, but he points out that screening is also crucial for detecting cancer early. In a recent review, he concluded that women with the BRCA1 mutation face a stark choice: their best hope may be to have both breasts removed. 鈥淭hese women have a choice between surgery and regular screening, and they must be aware of the risks of both.鈥�
Magnetic resonance imaging is another possible alternative to mammography, whose effectiveness for women under 50 has been questioned (see 快猫短视频, 26 October, p 27). Researchers at the Norwegian Institute of Technology in Trondheim claimed this week to be the first to use magnetic resonance spectroscopy to distinguish benign from cancerous breast tumours.