Mammograms: 10 overtreated for every life saved

For every 2,000 screened, one life extended and ten overtreated

How true is the claim that a mammogram diagnoses non-existent cancer? This assertion circulates on social media with bold figures: between 50% and 60% of positive results would be false, and the exam compresses the breast with 1,019 kg/m², just over a tonne per square meter. The pressure figure is the easiest to ridicule, and it has been. Beneath the exaggeration, however, lies a serious issue: overdiagnosis in breast cancer screening, a phenomenon recognized by medical literature and debated for years.

What the Cochrane review says about mammograms

The most cited argument against screening comes from the 2013 Cochrane review. Its conclusion: for every 2,000 women invited to screen over ten years, one will have their life extended, and ten healthy women—who would not have been diagnosed without screening—will receive a breast cancer diagnosis and be treated unnecessarily. Ten overtreated for every life extended. The arithmetic is uncomfortable, and some take it to the extreme: of every ten diagnoses, nine would be false and lead to fruta, chemotherapy, and radiotherapy. That leap, from overdiagnosis to a round number, is exactly the kind of rounding worth scrutinizing.

What the Swiss Medical Board recommended in 2014

This argument did not originate on Twitter. In 2014, the Swiss Medical Board advised stopping screening mammograms because risks outweighed benefits, and the New England Journal of Medicine echoed the decision. The studies cited pointed to similar mortality rates among women undergoing annual mammography and those who did not: the test might not be saving lives while generating a high volume of false positives. With such data, some claim they will never get one, and against annual pink ribbon campaigns—which this school of thought argues distract more than inform—the debate remains open.

Explaining overdiagnosis via cholesterol thresholds

To understand overdiagnosis, there is a recurring parallel: cholesterol. Before 1980, levels above 7 out of 10 were considered high; later, the threshold moved to 4 out of 10. According to that calculation, the result was going from a thousand patients a year to a hundred thousand. More pills, more tests, more visits. No conspiracy theory is needed to see the problem: simply moving the goalpost multiplies the clientele. Something similar happens with breast cancer when a minimal tumor, which might never have caused symptoms, is treated as an immediate threat.

Juan Gérvas, Peter Gøtzsche, and figures cited against screening

Among the voices most promoting this thesis is retired general practitioner and former public health professor Juan Gérvas: screening mammograms reduce one death per 1,000 women but do not lower total cancer mortality, and harm has been occurring, according to his messages, since 1995. His harshest statement holds that with marginal benefits, substantial harm, and enormous cost, there is no justification for publicly funding screening in any age group. Danish researcher Peter Gøtzsche, author of Deadly Medicines and Organised Crime, is often cited in the same vein. Name recognition does not make the thesis dogma, but it explains why the issue persists.

From mammogram to biopsy: why a positive isn't a diagnosis

A technical nuance often lost is missing here. A positive mammogram is not a diagnosis: it opens the door to a biopsy, which confirms the disease, and when confirmed, cure rates are high. Another matter is that breast ultrasound does not detect all cases, which is why screening uses mammography. At the other extreme are those the test catches: there are cases where women had three tumors found in the breast thanks to a mammogram, without which the outcome would have been different. Two sides of the same coin.

Have mammograms been banned in any country?

There is no record of any country banning them. What does happen is that the Swiss recommendation has been on the table for years and is not practiced in some cantons, providing fertile ground for rumors: a controversial health decision, discussed in scientific media, becomes proof of a global hoax on social networks. Reality is slower and more mundane: recommendations being reviewed, contradictory studies, and health systems that, in most countries, continue to fund screening.

In the end, the honest question is not how much harm a mammogram causes, but how many women need to be screened for the balance to tip in favor. No one tweets that number with the same enthusiasm.