By Peter C. Gøtzsche at Brownstone dot org.

I dedicate this article to all women invited to mammography screening and those who love them because the public has consistently been lied to, for over 40 years. In invitations to screening, women have been told that by detecting cancers early, screening saves lives and leads to less invasive surgery. I shall demonstrate that all three statements are wrong.

Women are still being told these lies, by professional associations, screening advocates, screening researchers, cancer charities, and national boards of health. The American Cancer Society declares in a headline that "Mammography Saves Lives" and claims, with no references, that results from many decades of research clearly show that women who have regular mammograms are less likely to need aggressive treatments like surgery to remove the entire breast (mastectomy).

Screening Does Not Save Lives

In the randomised trials of mammography screening, the risk ratio for overall mortality after 13 years of follow-up was 0.99 (95% confidence interval 0.93 to 1.03) for those trials with adequate randomisation. The estimate happened to be the same for the other trials, some of which were so poorly randomised that the average age in the two compared groups was not the same, which makes an analysis of overall mortality unreliable.

For two of the three adequately randomised trials, those from Canada and the UK, there are follow-up data after 25 and 23 years, respectively. The risk ratio for overall mortality was 1.01 (95% confidence interval 0.98 to 1.03) for all three trials (both with a fixed effect and a random effects model, Comprehensive Meta Analysis Version 3.0). In the table, the year means the year the trial started:

This is a very strong result as it is derived from a total of 25,046 deaths. We can therefore say with great confidence that mammography screening does not save lives.

If we restrict the analysis to the two trials with a very long follow-up, the result is the same, a risk ratio of 1.01 (0.99 to 1.04).

Breast Cancer Mortality Is a Seriously Flawed Outcome

It will surprise most people to learn that we cannot trust what has been reported in the randomised trials about the effect of screening on breast cancer mortality but this is an objective fact.

A minority of the women who died were autopsied, and in several trials, cause of death was not assessed blindly. I have documented that assessment of cause of death was seriously biased. If we include all trials in the analysis, we would expect to see the greatest reduction in breast cancer mortality in those trials that were most effective in lowering the rate of node-positive cancers (cancers that had metastasised) in the screened group.

This was indeed the case, but the regression line was in the wrong place. It predicts that a screening effectiveness of zero (i.e. the rate of node-positive cancers is the same in the screened groups as in the control groups) results in a 16% reduction in breast cancer mortality (95% confidence interval 9% to 23% reduction). This can only happen if there is bias, and further analyses showed that assessment of cause of death and of the number of cancers in advanced stages were both biased in favour of screening.

Systematic reviews that include all the trials, also the poorly randomised ones, have reported that mammography screening reduces breast cancer mortality by 16-19%. As this estimate is of the same size as the bias in the regression analysis, this suggests that screening does not lower breast cancer mortality.

Another reason why breast cancer mortality is a flawed outcome is that screening leads to overdiagnosis, which is the detection of cancers and precursors to cancer (carcinoma in situ), which would not have come to the attention of the woman in her remaining lifetime and therefore would not have become a problem without screening. Since it is not possible to distinguish between harmless cancers and dangerous ones, they are all t...