17.07.2025 / Gerd Gigerenzer

The “Unstatistic of the Month” for July is the systematic misinformation about mammography screening. A prominent example shows how supposed successes are exaggerated and potential harms are concealed — to the detriment of informed patient decisions.

From the public broadcaster ARD to the tabloid newspaper BILD, German media reported on a new study by the University of Münster on the effectiveness of mammography screening. Press releases from the university, the Federal Office for Radiation Protection, and the Federal Ministry of Health proclaimed an impressive figure: "Among women who participated in the screening, breast cancer deaths fell by between 20 and 30 percent. “ The National Association of Statutory Health Insurance Physicians — a sponsor of the screening program — also announced the same figure under the headline ”Mammography screening saves lives.“ And BILD believes: ”For the past 20 years, mammography screening in Germany has been proven to save lives."

What the scientific data really show

The reality is different: Since the introduction of mammography screening, women have been systematically misled about its benefits and harms — not least because it is a billion-dollar source of income for radiologists, clinics, and equipment manufacturers. The figure of 20 to 30 percent is the most recent example. Before we pin down the origin of these figures, what do the best scientific studies say — in particular the eight existing randomized controlled trials involving a total of around 500,000 women?

1. Life expectancy: There is no evidence that women who participate in screening live even one day longer than those who do not.

2. Cancer mortality: Overall cancer mortality — including breast cancer — is the same in both groups.

3. Breast cancer mortality: Of every 1,000 women between the ages of 50 and 69, around five die of breast cancer over a period of about 11 years if they do not participate in screening. In the screening group, the figure is four. However, at the same time, one more woman in this group dies of another type of cancer – which explains why the overall cancer mortality rate remains unchanged (see point 2).

4. Risks of screening: In addition to (low) radiation exposure, there are two significant risks:

• Approximately one in ten healthy women receives a false-positive result, which leads to unnecessary anxiety, further examinations, or biopsies.

• Some women are diagnosed with cancer even though they have very slow or non-progressive cell changes that would never have caused any symptoms during their lifetime and they undergo unnecessary breast tissue removal or even complete mastectomy (see the following fact box from the Harding Center for Risk Literacy at the University of Potsdam).

Conclusion: Mammography screening does not save lives.

Former Federal Minister of Health Karl Lauterbach, who introduced the screening program together with former Federal Minister of Health Ulla Schmidt, has since expressed criticism. Lauterbach told SPIEGEL: “All new findings tend to speak against screening.” It is time to reevaluate breast cancer screening. Other politicians should follow suit and admit that introducing it was a mistake. Switzerland has already changed course. Currently, statutory health insurance companies spend around one billion euros annually on the program. They could use these funds more effectively in areas where lives are actually saved.

These two crucial pieces of information — that there is no evidence that screening prolongs life expectancy or reduces the likelihood of dying from cancer — are rarely communicated to women in Germany. Even media reports on the current Münster study did not clarify this.

The trick with relative risks

So how did we arrive at this supposedly spectacular reduction in breast cancer mortality of 20 to 30 percent? This figure is by no means new. When mammography screening was first introduced, the then Minister of Health Ulla Schmidt used this figure in the screening campaign.

Nor is the statistical trick new: Only the reduction in breast cancer mortality is reported. What is omitted is that mortality is reduced from 5 to 4 per 1,000 women, i.e., by 1 in 1,000, or by 0.1 percentage points (see point 3). Instead, this effect is presented as a relative reduction of 20 percent (from 5 to 4), often rounded up to 30 percent. This presentation dramatically exaggerates the tiny effect.

The “20 to 30 percent” communicated in the press releases of the University of Münster, the Federal Office for Radiation Protection, and the Federal Ministry of Health are therefore not only misleading but also constitute a clear violation of the long-established standards of evidence-based health communication, which are regularly adhered to by many other actors in the health system and critical journalists.

Honest information

In its first brochures, German Cancer Aid advertised a relative risk reduction of 20 to 30 percent. Around 2010, Unstatistik author Gerd Gigerenzer worked with German Cancer Aid. Together, they removed the relative risks — along with the misleading five-year survival rates — from its information brochure on breast cancer and replaced them with understandable absolute figures. Today, the brochures no longer contain relative risks, and information about disadvantages is also provided.

However, even the best information materials continue to exaggerate the benefits of screening, as shown by the current brochure from the Joint Federal Committee, which is sent to women throughout Germany. It does not state that screening does not prolong life, nor that 1 in 1,000 fewer women die of breast cancer. Instead, it says: “3 to 8 out of every 1,000.” How did this come about? Apparently, the effect, which has been proven for a period of about 11 years, was extrapolated linearly to 25 years — without sufficient scientific basis. The only study that tracked the effect over 25 years (with 100,000 women), by contrast, found no reduction in breast cancer mortality through screening programs.

Informed decisions require complete information

Tagesschau online emphasizes that “every woman can decide for herself.” But how is it possible to decide when the results presented are incomplete and distorted?

Women and women's organizations should intervene here. Leading media outlets such as ARD and institutions such as the Ministry of Health must finally take a clear stand on the side of science — and ensure that women can make truly informed decisions.