Why mammography screening doesn’t and cannot work

And how cancer charities deliberately disinform the public

In my article about screening for prostate cancer, I noted that cancer charities and cancer researchers routinely publish misleading survival analyses that include many overdiagnosed, harmless cancers that would never have come to the patients’ attention in their remaining lifetime without screening. It seems to be a deliberate strategy to deceive the public into believing that important progress is being made in the fight against cancer.¹ In this article, I shall explain that 5-year survival rates in observational studies of cancer are also used to disinform the public.

There is no shortage of examples of invalid results receiving undue attention in the media.² Mike Richards and colleagues published a particularly misleading article in the BMJ in 2000.³ And Richards is not just anyone. He is a British oncologist; was the National Cancer Director from 1999 to 2013 in the UK Government’s Department of Health; and was knighted in 2010. You don’t get a knighthood if you tell the truth about cancer screening, which my colleague, British breast surgeon Michael Baum, is a good example of.¹

Richards and his co-authors wanted to estimate the number of lives saved because of cancer screening and improved treatment of cancer by comparing two time periods in England and Wales. This is very simple to do: Count the current number of cancer deaths for each cancer and compare it with the expected number by extrapolating the time trends in an earlier time period. However, the authors looked at 5-year survival rates and their study was torn to pieces in the BMJ letters that followed, including one from Michael Baum.⁴

People experienced in cancer surveillance, statistics and public health were among the authors, and one came from a “Cancer Intelligence Unit,” which is amusing for a study that is unintelligent. The starting point for their research was the government’s target about reducing cancer mortality by at least 20%. It was therefore inexcusable that the authors did not look at exactly that: cancer mortality. Instead, they deliberately misled the public.

Why 5-year survival rates are misleading

In randomised trials, 5-year survival rates are not misleading. The randomisation ensures that the two groups are comparable to begin with and there is therefore no problem in comparing the number of survivors after 5 years.

In observational studies, however, the clock is rarely started at the same time. If, for example, there is screening in one group and not in the other, the diagnosis will, on average, be made earlier in the screened group and the 5-year survival will automatically be better even if the patients in the two groups die at the same age, on average.

Moreover, screening leads to overdiagnosis of harmless cancers, which by definition means that 100% of the patients will survive their cancer. This introduces a huge bias.² As an example, the Malmö mammography screening trial reported a small, nonsignificant reduction in breast cancer mortality of 4%. If we limit the analysis to those with a diagnosis of breast cancer, we will spuriously find that screening reduced breast cancer mortality by 28%.

Nonetheless, the scientific literature is full of such erroneous estimates.² Fraud is a deliberate intent to deceive, and since those who published the studies virtually always knew better,² by far most articles are fraudulent.

Danish examples of fraud

Being Danish, I have followed particularly closely all the fraud and disinformation that have been propagated in my country. As it is pervasive and consistent also in other countries,² we are seeing a worldwide, systematic deception of our citizens, journalists, and politicians.

Here is an example.⁵ In 2002, a PhD dissertation supported by the Danish Cancer Society reported that the 5-year survival was 83% in a county with screening and 77% in two counties without. The author said the numbers speak for themselves; it was frontpage news that screening saves lives, and the top politician for health in the Danish counties advised that screening be introduced in the whole country, supported by the director for the Danish Cancer Society.

However, one of the examiners for the dissertation noted six days after the thesis defence that such comparisons are problematic, and I explained that they are totally misleading.⁶

If we use a little algebra, we can easily work out how much overdiagnosis there would need to be to arrive at the two percentages, assuming screening does not lower breast cancer mortality. Since overdiagnosed tumours have 100% survival, we add them to both the numerator and the denominator and find that an overdiagnosis of 35% can explain the seemingly better survival in the county with screening: (77 + x)/(100 +x) = 0.83 → x = 35.

Next, let’s look at how large the overdiagnosis caused by screening is. Denmark is a unique country for studying overdiagnosis because we had a period of 17 years (1991-2007) where only about 20% of potentially eligible women were invited to screening because some counties did not have screening. We found 33% overdiagnosis,⁷ corresponding to what was needed to produce the spurious effect of screening in the thesis.

Thus, what the dissertation really showed was that screening had not reduced breast cancer mortality, which we confirmed in another study of Danish women where we did not find any effect of screening.⁸ The decline in breast cancer mortality in women who could benefit from screening was 1% per year in the screening areas and 2% per year in the non-screening areas. The decline was 5% per year in women who were too young to benefit from screening in the screening areas, and 6% per year in the non-screening areas in the same time period.

In my critique of the dissertation, I noted that the Danish Cancer Society should be concerned about its credibility,⁶ but they didn’t heed my advice. In 2008, a Danish newspaper announced that the 5-year survival had “increased from 60% to 80% in 30 years.”⁹ Henning Mouridsen from the Danish Breast Cancer Group and Hans Storm from the Danish Cancer Society said that this was due to better treatments and screening. They forgot to say that an improvement in the 5-year survival rate over a time span of 30 years is highly misleading.

Over such a long time span, the problem is not just overdiagnosis. Another issue is increased breast cancer awareness. In Denmark, the average size of the tumours was 33 mm in 1978-1979, which had decreased to 24 mm ten years later.¹⁰ This was before screening even started.

My studies of tumour sizes and stages in the randomised trials showed that the trials were considerably biased in favour of screening.^2,11,12 It was simply not possible to obtain the survival benefits that had been reported.

I demonstrated that those trials that reported the greatest reduction in advanced cancers with screening also had the biggest reduction in breast cancer mortality, which would be expected if screening worked, but there was a problem and it was huge.¹²

The linear relation between advanced cancers and breast cancer mortality was in the wrong place. A screening effectiveness of zero, meaning that the rate of node-positive cancers is the same in the screened group as in the control group, corresponded to a highly significant 16% reduction in breast cancer mortality (P < 0.001). My further analyses demonstrated that assessment of cause of death and of the number of cancers in advanced stages were both biased in favour of screening. And since the size of the bias, 16%, was similar to the estimated effect of screening, including all the trials, even the very poor and biased ones, this result suggests that screening is ineffective.

Lying to the public with no shame

In 2009, a newspaper reported that Denmark had the highest death rate in breast cancer among the OECD countries.¹³ The Danish Cancer Society didn’t miss the golden opportunity to deceive the whole population once again. Chief physician Iben Holten said that we found cancer too late, and chief statistician Susanne Møller added that Denmark had not had nationwide screening, in contrast to Sweden where the women were diagnosed earlier and therefore had better survival rates.

Two of the five regions in Denmark had still not started screening, and Holten was very sorry about this because, as she said, those cancers that were not found by screening have a far worse prognosis.

Holten was highly dishonest. Everyone who works with cancer screening knows that those cancers that grow rapidly tend to be missed between two screenings. It is called length bias, and it means that screening preferentially detects slower-progressing, less aggressive tumours with better prognoses.

Four years later, senior statistician Gerda Engholm from the Danish Cancer Society contributed to the disinformation.¹⁴ She said in an interview that the lower survival rates for Danish women with breast cancer compared to other countries was largely because 80% of Danish women had not been offered mammography screening.

Engholm argued that three years after the diagnosis was made, 89% of Danish women were

alive, compared to 91-94% in Norway, Sweden, Canada and Australia. I noted that she knew perfectly well that she was spreading misleading propaganda contrary to the facts,¹⁴ as the mistake she made was so basic that it was known by everyone involved with cancer screening (just as Holten could not have been unaware of length bias). Moreover, in the UK, which introduced screening in 1988, the three-year survival rate was only 87%, i.e. lower than in Denmark, but this information was not offered by Engholm.

I had pointed out these basic issues several times to the Cancer Society, also to Engholm, e.g. in our medical journal, when the Society came up with its misleading propaganda, yet they continued to defraud the public. I therefore ended my article by asking: “Does the Cancer Society have no shame?”

No. People who propagate falsehoods about breast cancer to benefit themselves have no shame. In 2026, there was an article on a Danish science site that was equally misleading as all the others.¹⁵ We were told that 5-year survival in Denmark is now almost the same as in Sweden, and breast surgeon Niels Kroman explained that Danish women received the same good treatment as in Sweden. A bar chart showed that, earlier, 5-year survival was poorer in Denmark. Nowhere was there any information that the improved 5-year survival is misleading because Denmark introduced screening in this period, which added a lot of survivors “for free.”

About 25 years ago, I had a folder labelled “Dishonesty in breast cancer screening,” where I stored articles and letters to the editor that contained statements I knew were dishonest. I had planned to write a paper about this collection, but the number of examples quickly exceeded what could be contained in a single article. This was the basis for the first of my two books about mammography screening.^2,5

The three worst lies

All over the world, cancer charities and cancer researchers have sold mammography screening to the women with the argument that it saves lives and breasts by early detection. None of this is true.

If we assume that the observed doubling times for breast cancers are constant, it means that the average woman has harboured the cancer for 21 years before it becomes detectable at breast screening, at about 10 mm in size.¹¹ This is not “early detection.”

For several reasons,^2,5,16,17 breast cancer mortality is a biased outcome that favours screening, and the trials show that total cancer mortality, including breast cancer mortality, and total mortality are not reduced.^17,18 After 600,000 women had participated in the trials and after decades of follow-up, the risk ratios were 1.00 for cancer mortality including breast cancer and 1.01 for total mortality.¹⁸ This is not “saving lives.”

Because of the considerable overdiagnosis and because the earliest cell changes that can be seen on a mammogram, carcinoma in situ, are often diffusely spread in the breast, and sometimes in both breasts, screening has the effect that more women lose one or both breasts.^2,5,19 This is not “saving breasts.”

When will this madness stop?¹⁶ And why do cancer charities, cancer researchers and many others lie so profusely about the facts and continue doing so after their errors have been pointed out to them? Even the once highly respected Cochrane Collaboration has now joined the disinformation camp, indeed to such a degree that they refused to let us update our Cochrane review of mammography screening with more mortality data.¹⁸ This was editorial misconduct.²⁰

Mammography screening has caused many to lose a breast but even more to lose their head. Why can’t people see that the emperor has no clothes? When I published my first book about all the lies,² Iona Heath, President of the UK Royal College of General Practitioners, wrote in her foreword:

“If Peter Gøtzsche did not exist, there would be a need to invent him. He is a committed and meticulous scientist who has worked as a clinician and who delights in numbers and mathematics and what they can tell us, to an extent that is rare among doctors. He is also tenacious and refuses to tolerate the foolishness of wishful thinking.”

Would we have had screening today, if the politicians had known the facts? I doubt it. A comprehensive review from 2016 found no correlation at all between introduction of screening, which could be more than 20 years apart in similar countries and states, and the decline in breast cancer mortality that in all cases began in the early 1990s, which coincided with the introduction of tamoxifen treatment.²¹

In 2017, my research group showed that screening in Denmark was not associated with lower incidence of advanced tumors.²² When this is the case, screening cannot possibly lower breast cancer mortality.

Which country will be first to stop mammography screening? It is total madness to allow this.

References

1 Gøtzsche PC. Why you should not get screened for prostate cancer. The American Cancer Society misleads the public and enrich themselves. Substack 2026;March 16.

2 Gøtzsche PC. Mammography screening: truth, lies and controversy. London: Radcliffe Publishing; 2012.

3 Richards MA, Stockton D, Babb P, et al. How many deaths have been avoided through

improvements in cancer survival? BMJ 2000;320: 895-8.

4 Letters. BMJ 2000;321:1470.

5 Gøtzsche PC. Mammography screening: the great hoax. Copenhagen: Institute for Scientific Freedom; 2024 (freely available).

6 Gøtzsche PC. Kræftens Bekæmpelse, screening og troværdigheden. Ugeskr Læger

2003;165:611-2.

7 Jørgensen KJ, Zahl P-H, Gøtzsche PC. Overdiagnosis in organised mammography screening in Denmark: a comparative study. BMC Womens Health 2009;9:36.

8 Jørgensen KJ, Zahl PH, Gøtzsche PC. Breast cancer mortality in organised mammography screening in Denmark: comparative study. BMJ 2010;340:c1241.

9 Tougaard H. Flere kvinder overlever brystkræft. Jyllands-Posten 2008;May 21.

10 Rostgaard K, Vaeth M, Rootzén H, Lynge E. Why did the breast cancer lymph node status distribution improve in Denmark in the pre-mammography screening period of 1978–1994? Acta Oncol 2010;49:313-21.

11 Gøtzsche PC, Jørgensen KJ, Zahl PH, Mæhlen J. Why mammography screening has not lived up to expectations from the randomised trials. Cancer Causes Control 2012;23:15-21.

12 Gøtzsche PC. Relation between breast cancer mortality and screening effectiveness: systematic review of the mammography trials. Dan Med Bull 2011;58:A4246.

13 Hansen JH. Danmark har den højeste dødsrate for brystkræft. Information 2009;Dec 9.

14 Gøtzsche PC. Vildledning fra Kræftens Bekæmpelse om mammografiscreening. Ugeskr Læger 2013;175:1056.

15 Rasmussen MK. Hvor gode er vi til at behandle brystkræft i Danmark? Videnskab.dk 2026;Feb 17.

16 Gøtzsche PC. Mammography screening is harmful and should be abandoned. J R Soc Med 2015;108:341-5.

17 Gøtzsche PC, Jørgensen KJ. Screening for breast cancer with mammography. Cochrane Database Sys Rev 2013;6:CD001877.

18 Gøtzsche PC. Cochrane on a suicide mission. Brownstone Journal 2025;June 20.

19 Jørgensen KJ, Keen JD, Gøtzsche PC. Is mammographic screening justifiable considering its substantial overdiagnosis rate and minor effect on mortality? Radiology 2011;260:621-7.

20 Gøtzsche PC. Cochrane editorial misconduct: our review of mammography screening. Substack 2026;Jan 17.

21 Bleyer A, Baines C, Miller AB. Impact of screening mammography on breast cancer mortality. Int J Cancer 2016;138:2003-12.

22 Jørgensen KJ, Gøtzsche PC, Kalager M, Zahl PH. Breast cancer screening in Denmark: a cohort study of tumor size and overdiagnosis. Ann Intern Med 2017;166:313-23.