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Mammography screening

October 30, 2012

One breast cancer death prevented for three overdiagnoses

The government-appointed independent panel reporting in today’s Lancet (click here) estimates the harms from the breast screening programme as follows:

“For every breast cancer death prevented, about three overdiagnosed cases will be identified and treated”.

It is an excellent report, and this is the best estimate possible. It is the basis for headlines all over the press, presumably spun by the screening mafia, that “breast cancer screening saves lives” (e.g. here), albeit at the cost of a few unnecessary mastectomies. But note the careful wording “for every breast cancer death prevented …”.

The panel based their findings on the Cochrane review which estimated a relative risk for breast cancer mortality from screening of 0·80 (95% CI 0·73–0·89), i.e. a 20% reduction.  But they ignored the same Cochrane review evidence on all cause mortality, on the grounds that “all-cause mortality is not an appropriate outcome for trials of breast screening because the trials were not designed with sufficient power for this outcome.”

True, but women contemplating joining a screening programme, which is going to remove or irradiate three breasts for every breast cancer death prevented, might be interested. So here it is – click here for details – a relative risk for all cause mortality of 0.99, (95% CI 0.95 to 1.03).  i.e. no measurable effect.

Screening enthusiasts typically respond that, since deaths prevented by screening form such a tiny proportion of the total, it would be unreasonable to expect the trials to show an effect. They are probably correct, although it is also plausible that at least some of the apparent reduction in breast cancer deaths is due to altered classification. But whatever our views about that thorny issue, screening enthusiasts must agree that if the benefit is so easily swamped by other causes of death, and is causing all this over treatment, it can hardly be providing a major net public health benefit.

Ideally the NHS should close down the breast screening programme and spend the money on more important priorities. Let women decide for themselves whether the benefits outweigh the harms sufficiently to justify the cost, and if so buy private screening.  Most well-informed women, particularly those without  obvious risk factors, would choose not to.

Vested interests will keep the NHS programme going, but they must now stop bullying women to join up.

Jim Thornton

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