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Breast screening risks outweigh benefits says Baum

Breast cancer expert remains concerned by harms from overdiagnosis

Louise Prime

Thursday, 24 January 2013

The harms of breast screening outweigh its benefits, believes breast cancer expert Michael Baum. The professor emeritus of surgery at University College London has written a personal view in today’s BMJ in which he argues that the number of lives saved by screening is more than outweighed by deaths caused by long-term adverse effects of treatment.

Professor Baum, who for many years has spoken out against mammographic screening, says he remains unconvinced by the conclusions of Sir Michael Marmot’s committee published last November. The committee had been tasked with deciding whether or not the screening programme should continue and, if so, what women should be told about overdiagnosis before deciding whether or not they would accept the invitation.

Marmot’s group reported an overdiagnosis rate of about 19% – 129 of 681 cancers detected in 10,000 women would have done them no harm during their lifetime – meaning that those women were subjected to unnecessary treatment including surgery, chemotherapy and radiotherapy. This was higher than previous estimates of the rate of overdiagnosis. Nevertheless, the committee advised that the screening programme should continue because, they said, 43 deaths from breast cancer were prevented per 10,000 women invited for screening.

Baum disputes this figure because, he points out, advances in breast cancer treatment and in women’s chances of survival after diagnosis reduce the benefits of screening – raising the risk of overdiagnosis to about 50%. He argues: “The two key points are that, as systemic therapy improves, the window for the impact of screening narrows substantially, and as overdiagnosis rates increase then the importance of the relatively rare lethal toxicities of treatment increase.”

Research published in the BMJ today found that most women invited for screening would accept if told that the overdiagnosis rate was 30% or lower, but most would reconsider their decision if told that the rate was as high as 50%.

Baum points out that screening reduces neither the rate of mastectomy, nor all-cause mortality; he says the Marmot committee chose to “duck” the question of whether or not screening lengthens life overall by focusing instead on cause-specific mortality.

He estimates that three or four breast cancer deaths are avoided by screening, for every 10,000 women invited, but 2.72 to 9.25 deaths are caused by radiotherapy’s long-term effects. He concludes: “I crudely estimate that an additional one to three deaths might be expected from other causes for every breast cancer death avoided.”

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