Are breast cancer screening programs justified?

Millions of Canadians happily sign up for breast cancer screening every year. After all, we’re told that it “saves lives” for women aged 50 to 74.

Yet, there is no evidence that it does. Most – but not all – studies conclude screening mammography reduces a woman’s chance of dying of breast cancer. But in randomized controlled trials on breast cancer screening tests, those who received the screening didn’t live longer than those who weren’t screened.

There could be many reasons for this. One is that there are many, many causes of death. It’s extremely difficult to prove that slightly reducing just one of those causes decreases mortality rates overall. “You’re into a substantial numbers problem,” says Anthony Miller, an epidemiologist and professor emeritus at the Dalla Lana School of Public Health in Toronto. It’s possible mammography screening does save lives but the life-saving benefit is so small and the trials so far haven’t followed enough patients to prove it.

There is, however, a more concerning theory as to why mammography screening doesn’t seem to extend lives: that the harms of breast cancer screening could offset the benefits.

According to an independent UK panel, for every one breast cancer death that annual mammography prevents, at least three women will undergo unnecessary treatment because cancers will be found that wouldn’t have caused problems if left alone. This treatment can involve surgery, chemotherapy and/or radiation. The latter two treatments can damage the heart or even cause other cancers, explains Peter Jüni, Director of the Institute of Primary Health Care at the University of Bern in Switzerland. One of the reasons breast screening doesn’t affect overall mortality in trials could be that “deaths through cardiovascular causes would probably be increased in those unnecessarily treated for breast cancer,” he says. Radiation exposure from breast cancer treatment could also lead to other cancers – interestingly, mammography screening doesn’t seem to reduce a woman’s risk of dying of cancer in general.

So why does Cancer Care Ontario’s website state that breast screening saves lives? The message is “intended to be understood by a lay audience,” explains Linda Rabeneck, vice president of prevention and cancer control at CCO. “Frankly, a more correct statement would say it reduces the risk of a woman dying from breast cancer.” Decreasing one’s risk of dying of breast cancer isn’t the only reason to get mammography screening, however. “If you’re diagnosed at an earlier stage, the cancer may be dealt with surgically and you may not need to have chemotherapy or radiation,” Rabeneck says.

Do the sicknesses and deaths prevented by breast cancer screening outweigh the sicknesses and deaths caused by unnecessary breast cancer treatment? Most think it does, but not all experts agree. And the controversy is not new, as Healthy Debate’s previous articles on mammography make clear.

Marcello Tonneli, chair of the Canadian Task Force on Preventative Health Care thinks the benefits of cervical, breast and colon cancer screenings outweigh the risks for the recommended age groups. Still, he says, “there is often naïve enthusiasm for screening” among health experts and patients alike.

Risk-benefit conversations still not happening

Rabeneck explains that CCO now encourages doctors to have more nuanced conversations around the positives and negatives of routine mammography with patients, based on “a new understanding of the evidence” whereby the benefit-to-harms ratio of mammography screening is lower than what was previously thought. In addition to the risk of unnecessary treatment, almost 30% of women above 50 who are screened over a decade will receive a false positive result, leading to further testing and psychological stress.

“[Health providers] inform a woman of the potential benefits and harms, and she gets to make her own decision, we don’t inflict [mammography] on anyone…she can opt out,” says Rabeneck.

But at least some doctors still aren’t talking to women about harms, according to experiences we’ve heard from Canadian women. Earlier this month, for example, Diane*, an Oakville, Ontario-based writer, went for her 50-year-old physical and was told it was time for her to have her first mammogram that would be covered by the province.  “The doctor just said ‘Okay, you’re due for a mammogram and here’s your requisition.’ I didn’t question it.”

Two years ago, Leslie*, a mother of two living in Toronto, was told she should have mammogram screening at 52. “They certainly didn’t educate me on any risks for or against,” says Leslie. And when she presented her health provider with the evidence that the benefit of routine mammography is extremely small, “it just was like, ‘We’re not going to have this conversation.’” Leslie opted out of screening. “I had a cousin who ended up dying of leukemia, likely caused by the [radiation] that she received for breast cancer treatment. So that obviously swayed my vision as well.”

There are several other reasons these conversations aren’t always happening. One is that new understandings of risks and benefits can trickle down slowly, and doctors might simply be unaware of the numbers, says Miller.

Another is that, despite CCO’s expectation of doctors to fully inform patients, the organization’s  patient information could send the message that it’s not important to talk about risk. CCO’s mammography brochure for doctor’s offices was updated in 2014 and now mentions the risk of unnecessary treatment, but no numbers are provided and false positives aren’t mentioned. In total, there are only two sentences about harm in a two-page, small-print brochure.

And the website still pushes routine mammography. Case in point: Several videos aimed at newcomers that don’t mention risk at all. ‘Vanita came to Canada from India…The doctor told her that if breast cancer is caught early, it is easier to treat. She gets tested regularly and encourages her friends to do the same,’ one video description reads. (The Canadian Task Force on Preventative Care’s website is much more objective.)

In a presentation last week, Dr. Cathy Risdon, associate chair of the department of family medicine at McMaster University and a practicing physician, said she feels “uncomfortable” with the fact “that there is not another side” in CCO’s letters to women on mammography screening. While noting there “are many, many reasons that women still choose to receive screening,” Dr. Ridson thinks women over 50 should also be told that “choosing not to screen is very sane and can be very consistent with caring for your health.” She supports either choice a patient makes.

For other physicians, financial incentives could tip the balance in favour of mammography screening. Most doctors in Canada are at least partly paid per service provided. And one long conversation on risks and benefits can take as much time as several quick screening referrals, while netting a much smaller payment. The Ontario government additionally pays doctors a $2,200 bonus per year if 75% of their eligible patients are referred for routine mammography. Alberta doesn’t have such an incentive but the government does have a mammography uptake target of 70% of eligible patients by 2020. (Currently, mammography screening participation rates in Ontario and Alberta are 60% and 56%, respectively, for women ages 50-74).

It’s more likely doctors have laudable reasons to oversell mammography, according to Doug Stich, program director of Toward Optimized Practice, the body that implements cancer screening recommendations in Alberta. “It’s a very real experience for a primary care physician to have a patient die of one of these diseases and to feel like they failed them and that they’re not going to let that happen again,” he explains.

Both doctors and patients are influenced by the stories we hear. People who develop organ problems or cancers often don’t trace it back to previous chemotherapy or radiation. But, explains Stitch, “patients who discover cancer through screening tend believe that the screening saved their lives.” Even if it didn’t.

Messaging around breast cancer screening should be more accurate

Some believe that given the changes in breast cancer treatment and advances in mammography, a new randomized controlled trial on screening mammography is crucial. Dr. Miller also points out it’s possible genetic research will reveal what types of breast cancers do not progress rapidly and it will therefore be clearer when treatment is necessary and when it’s not.

The evidence we have now, however, suggests that the benefit of mammography is small and the risks are not insignificant. Yet, poor information means most patients believe the benefit of mammography screening is much higher than it is. And if patients had more information, it’s quite likely fewer would opt for mammography. In a US study of 317 people, 51% of those polled said they wouldn’t want to be screened if screening leads to more than one unnecessarily treated person per one life saved.

Because comfort level with various risks differ by patient, in Alberta, Stich’s organization trains physicians that “a patient saying ‘I decided not to’ is equally as good a result as a patient saying ‘Yes, I will go ahead with the screen.’” But the Alberta government’s mammography target and the Ontario government’s mammography bonus send a message that patients should be sold on mammography screening.

Tonneli finds the incentives concerning. “We need to give people good information about the risks and benefits of screening, together with tools that help them to understand the information,” he says. “I worry that providing doctors with a financial incentive to screen more people is at odds with this goal.”

Peter Suter is chair of the Swiss Medical Board that recently recommended against routine mammography on the basis it “does not clearly produce more benefits than harms.” Suter thinks mammography screening should continue to be funded, but that it should be up to each woman to decide if she thinks the benefit outweighs the risk, or vice versa, in her particular case. (Someone with a family history of fatal breast cancer may be more likely to go for screening, for example.) “We need to stop saying mammography saves lives…this propaganda is borderline in terms of ethical issues,” he says.

*Names have been changed.

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  1. Joan Eakin

    I wonder if the ‘harms’ side of the ledger should also include potential harm from extra radiation of the mammograms themselves (original and repeats for ambiguous results), and more significantly (to me anyway), the physical trauma of the mammogram itself. I know from my own experience and speaking with other women that it can be extremely painful to have the breast crushed down like it is to get a good reading (my inquiries among colleagues a few years ago about the theoretical possibility of this kind of harm suggested some but no definitive confirmation of the possibility). Moreover, I wonder if physical trauma to the breast might be greater than it need be because the machines seem to be designed for a square linear box shape not a curvy rib-cage shape – and also made for an average size and not for smaller body frames (who designed these things anyway?? clearly not anyone with any understanding of female anatomy). Can medical disorder (even cancer) be triggered by the physical force of the mammography instrument?

    • Wendy Glauser

      Thanks for your comment, Joan. We didn’t mention radiation from the mammography screening itself as this risk seemed quite small in comparison to the harms of anxiety from false positives and harms of over-treatment. (Of course, one could write a book on the risks versus benefits of breast cancer screening). I agree with you, however, that the radiation from screening should also be mentioned in discussions with patients. The Public Health Agency of Canada talks about radiation from screening mammography under “Are mammograms safe?” here:

      I have heard the pain and discomfort of the test being cited as a reason women choose not to repeat screening mammograms so that aspect is important indeed!

  2. Charles J Wright

    Finally, the truth about screening mammography, namely the lack of benefit and the substantial harm caused, is getting to the public and, hopefully, to the medical profession also. The most prestigious independent group investigating screening mammography (the Danish Cochrane Collaboration) has been publishing these findings for several years, but the powerful vested interests are lined up to deny the evidence. Although it was begun 4 decades ago with the best intentions based on hypotheses now known to be false, we have built what is now a large and dangerous industry. Large numbers of radiologists and radiographers are involved, supported by the surgeons, oncologists and pathologists that have to deal with the resulting fallout of over diagnosis, false positives and related unnecessary interventions. Politicians in our publicly funded system are understandably very unhappy at the prospect of dismantling the screening mammography programs that were launched with so much enthusiasm – although they should be encouraged by the huge resources that could be redirected in the process. And what about the public? We now have three generations of women who have been misled into thinking that mammography can “save” their lives. A very intensive but sensitive public education program at the least will be required. As for the medical profession it really is time to apply current research and hard evidence to current practice.

    • Wendy Glauser

      The financial stake is definitely worth considering, Charles. And yet, I think partly it’s as you say, once a preventative intervention has been met with such widespread enthusiasm, altering perceptions can be very difficult.

  3. Dr Martin Yaffe, breast cancer researcher

    I thought that your work was intended to be evidenced based. Yet this article is very clearly one-sided – biased against screening. The reduction of breast cancer mortality associated with screening has been demonstrated through multiple randomized trials (considered the strongest form of evidence) and backed up by modern observational studies. You didn’t even mention the work of Coldman et al. in Canada (published in the Journal of The National Cancer Institute, 2014) who showed breast cancer mortality reductions of 35% to 45% in women between 40 and 79 who participated in screening programs across Canada.
    Your statement that there is no evidence that breast cancer screening saves lives insults the intelligence of your readers. There have been no randomized studies designed to test the effect of screening on overall mortality. And, as the authors should know, such a trial would have to be enormous in the number of participants because most women (even women who had breast cancer) will eventually die of some other cause. Breast cancer screening reduces premature death from breast cancer and there is no evidence that in doing so it increases any other type of mortality.

    And upon what evidence is the “concerning theory” that screening has harms that offset mortality reduction from breast cancer based? If anything, cancers found earlier are less likely to need treatment with chemotherapy, in some cases a cause of cardiotoxicity.

    You quote Dr. Marcello Tonelli about the importance of accurate communication information about the benefits, limitations and harms associated with screening. I agree completely. But his own Task Force misinformed physicians and the public in their recommendations by underestimating the lifesaving efficiency of screening women in their 40s by over a factor of 3. It went on to and suggest that screening women over 50 could be done triennially without providing a shred of evidence.

    I have read all the literature about overdiagnosis and overtreatment. It is reasonable to suspect that they occur, especially for in situ cancers, but the estimates, which generally involve major assumptions, are all over the map – from 0 to 50% of cancers. There have been no studies designed to provide an accurate measure of the amount of overdiagnosis or overtreatment, i.e. there is no reliable evidence. And is the solution to this problem to ignore finding the lethal cancers earlier when they can be treated more effectively? Or should we instead focus on trying to avoid overtreatment?

    What are the credentials of the self-appointed Swiss Medical Board who recommended against routine mammography screening against the solid evidence of its benefit?

    Of course it should be up to each woman to make the decision as to whether she wishes to be screened. But she should be provided with accurate information. Your article, which is clearly slanted against screening, certainly does not contribute to a Healthy Debate on this subject.

    • Wendy Glauser

      Dr. Yaffe,
      Thank you for your comments. We do mention in the fourth sentence that most breast cancer screening trials do show a reduction in breast cancer mortality. We linked (through the word ‘most’) to a summary of this evidence. There have been trials examining the effect of breast cancer on overall mortality – see – but as you mention, and as we also mention in the article, it is highly plausible these trials simply weren’t large enough to show such a reduction.
      Re: “And upon what evidence is the “concerning theory” that screening has harms that offset mortality reduction from breast cancer based?”, this point was made in some of the interviews for this article. Also, please see an analysis from the Swiss Medical Board – – where the authors state, “In the worst case, the reduction was canceled out by deaths caused by coexisting conditions or by the harms of screening and associated treatment.” In the analysis to the Ioannidis paper, the authors state one of the reasons that studies haven’t found a decrease in mortality could be that “the risk-benefit ratio of the whole screening and treatment process is unfavourable.”
      I think most physicians see the Canadian Task Force on Preventative Health Care, of which Dr. Tonelli is the Chair, as the most authoritative and trusted source on screening recommendations so I think Dr. Tonelli is a legitimate source on this matter.
      The Swiss Medical Board’s website is in French and German, so I will refer you to this English language article - – which states: “The Swiss Medical Board is appointed and sanctioned by the Conference of Health Ministers of the Swiss Cantons (the country’s states), the Swiss Medical Association, and the Swiss Academy of Medical Sciences.”
      Evidence of overdiagnoses can be estimated based on how many more breast cancers are detected, at the end of a multi-decade study, in the screened group versus the unscreened group. You are right that the numbers of overdiagnoses and overtreatment vary by study, but so too does the reduction in breast cancer mortality vary by study. Dr. Anthony Miller’s RCT, for example, did not find a reduction in breast cancer mortality.
      We tried our best to represent the evidence for both arguments in this article – both that breast cancer screening is justified, and that it isn’t. We strive to strike the right balance in all of our articles but we also allow comments so that our readers can add their perspectives to account for the points they feel weren’t included. I thank you for your educated perspective on this important, and indeed contentious, issue.

      • Dr. Martin Yaffe

        Thanks for your response, Wendy.
        A few comments.
        1) Physicians and the public should be able to consider the advice of The Canadian Task Force on Preventive Health Care as reliable. Sadly, with respect to breast cancer screening this has not been the case. I mentioned the large error they made in estimating the number of women who would have to be screened to save a life. They were out by about a factor of 3! This is likely because they misunderstood a statistic that came out of the clinical trials literature. And in discussing harms, they implied that the harm associated with a woman being recalled for additional imaging when ultimately there is no cancer present, or that of a negative biopsy offsets the benefit of avoiding a premature death due to breast cancer or being able to have a cancer detected earlier treated without chemotherapy. They were comparing apples and grapes and this is inappropriate. Virtually every woman with whom I have discussed the issue told ne that she would be willing to exchange many “false positives” for an opportunity to have a cancer found earlier. Of course, we could do much better through more clear education about what it means to be called back after a screening exam and providing that second-level imaging as quickly as possible to minimize the stress.
        There were more lapses. None of the members of the Task Force had expertise in breast cancer or screening. Presumably this was to ensure that their guidance would be objective. The systematic review of evidence was not done by the Task Force but commissioned from another group and their document did not undergo peer-reviewed publication. All modern observational studies of breast screening were ignored. These are studies of effectiveness of screening in the real world. And although advice was offered to the Task Force by groups much more knowledgable than they on matters of breast screening (Canadian Breast Cancer Screening Initiative), such offers appear to have been largely ignored. So, no, Dr. Tonelli and the Task Force have not. in my opinion, been a reliable source of information.

        2) You mention Anthony Miller’s two studies (CNBSS), which found no reduction in mortality in comparing screening to no screening in women in their 40s and mammography plus physical exam to physical exam alone in women between 50 and 59. The other RCTs that did show mortality reduction achieved a reduction in the number of advanced cancers through earlier detection in the screened women. The CNBSS did not. This was almost certainly due to a surplus of women with advanced cancers who were initially assigned to the screening group, i.e. a problem with randomization. It would have been too late for these women to have benefited from screening. The other major problem was poor quality of the mammograms. These problems and others were clearly documented in a 1993 publication by Boyd et al. (Boyd NF, Jong RA, Yaffe MJ, Tritchler D, Lockwood G, Zylak CJ. A critical appraisal of the Canadian National Breast Cancer Screening Study. Radiology. 1993 189(3):661-3) and I discuss them again in an article that will appear in the June issue of Current Oncology.

        3) Finally, Dr Wright mentioned the Nordic Cochrane Group and its systematic reviews on breast cancer screening. Its director, Peter Gotzsche is a longtime avid opponent of screening. The reviews have been heavily criticized for their lack of objectivity and selective inclusion of any data that is negative on screening while ignoring evidence that is supportive of its value. (For more, please see: Freedman DA, Petitti DB, Robins JM. On the efficacy of screening for breast cancer. International Journal of Epidemiology 2004;33:43–55 ). Again, despite the prestige associated with The Cochrane Collaboration, I would not rely on Gotzsche’s work for guidance on screening.

        Mammography screening is far from a perfect tool for detecting breast cancer. As a researcher I could document many limitations. But, in conjunction with modern therapy, it helps reduce mortality and morbidity associated with breast cancer. My estimate is that there is the potential to save at least 1000 breast cancer deaths in Canada each year through screening.

        Rather than undermining confidence in something that has been proved in multiple studies to be effective, we should be using it thoughtfully to reduce deaths while working to improve upon it and eventually replace it with something better. We also should focus on finding ways to determine the most effective therapy for each cancer (precision medicine) to avoid over- or under-treating cancers that are found through screening.

  4. Jon

    Charles Wright, a scientists who long ago had pointed out the lack of real evidence for mass mammography, has also described here (again) what the real problem with the debates about mammography is: “powerful vested interests are lined up to deny the evidence.” The evidence of a lack of notable benefit and that the test does great harm.

    Yaffe has been working for the breast cancer imaging industry for many years. And, for many years he has been serving that industry in his ongoing denial of the great risks and little benefits of mammography. He’s true to that pattern in his comments here….

    IF women (and men) at large were to examine the mammogram data above and beyond the information of the mammogram industry (eg American Cancer Society, National Cancer Institute, Komen, their regular doctor), they’d also find that it is almost exclusively the big profiteers of the test (eg radiologists, oncologists, medical trade associations, breast cancer “charities” etc) who promote the mass use of the test and that most pro-mammogram “research” is conducted by people with massive vested interests tied to the mammogram industry. The study Yaffe cites in favor of mammography (“Coldman et al. in Canada (published in the Journal of The National Cancer Institute, 2014 “), for example, is led by people who are professionally involved in the breast screening business. It’s common that the people who perform the scientific studies on mammography never disclose that their well-paid members of this huge business, or affiliated businesses.

    The ‘big picture’ truth is that it’s almost all flawed, biased, corporate-crafted pro-mammogram studies that are in favor of the procedure. The most reliable evidence shows otherwise.

    So, among the sneaky unethical tricks of these people to denigrate dissenting voices is by asking spurious things like “What are the credentials of the self-appointed Swiss Medical Board who recommended against routine mammography screening against the solid evidence of its benefit?” as Yaffe did in his May 12th comment. Do people who have vested interests have more trustworthy credentials than capable people who honestly are trying to follow the scientific data? Why should you believe people who suppress their money connection to the mammogram business when they say there is no evidence that mammography increases overall mortality (or other risks)? Why should you believe people who suppress their money connection to the mammogram business when they say mammography is highly beneficial? Yaffe writes that women “should be provided with accurate information” but evidently that does not include for him and the mammogram industry to tell women about their vested interests tied to that business, knowing that vested interests severely corrupt the validity of scientific research and findings.

    The mammogram cartel consistently lies to you but they want you to blindly trust them in what they claim about mammography – based on their authoritarian credentials and assertions.

    The public still primarily gets to hear pro-mammogram information. Yet beyond this disinformation and propaganda systematically promulgated by the medical business everyone can easily find out what the real truth is about that test. The two most thorough, extensive, meaningful, independent accounts of the non-science of mammography, the large body of relevant anti-mammogram evidence that’s been ignored by the mammogram industry, and the huge influence of big money and politics on the dominant status of mass screening see “Mammography Screening: Truth, Lies and Controversy” by Peter Gotzsche and “The Mammogram Myth” by Rolf Hefti (TheMammogramMyth dot com). Once you read these accounts you will never look at mammography (or the medical profession) the same way ever. In view of the corrupt mode of operation of the mammogram supporters/profiteers, it should not surprise you that Yaffe advises you “not rely on Gotzsche’s work for guidance on screening.” Of course not, because you might find out the real truth.

    Luckily, more and more women (and men) have been waking up to the scam that mass mammography is. Hence, the falling numbers of women who attend screening.

  5. Anon person

    How many patients have been told by their family doctors that if they do not participate in cancer screening tests then they can seek primary care elsewhere?. “I can’t be your doctor if you don’t take these screening tests”. I know several people. They cannot get their medication for diabetes, pain, asthma or other chronic conditions without a family doctor.

    The incentive programmes for cancer screenings should be scraped. The money could be put to better use for patient care.

  6. vera

    You cannot opt out in Ontario, you are red flagged at your doctor’s office and will get a lecture, the same goes for cervical and colorectal cancer. Alberta gives you the opt out options but in Ontario you are a naughty child that is just not listening.

    • Vera

      I have tried complaining about forced screening to the Ministry of Health, the Privacy Commissioner of Ontario and was basically mocked and insulted by Cancer Care Ontario. They seem to rule the Ministry of Health now. I have trouble getting migraine drugs now because of their policy, one walk-in will give them to me. I won’t have any primary care until age 74 when the screening police stop. In Alberta I would have none of these issues. A grand total of 19 people in that province excluded themselves from screening. I have an anxiety disorder and cannot live with a cloud of screening over my head all the time but that is ignored as only normal women who do what they are told, and have no anxiety disorders, are worthy of any health care in this province. I don’t have any private options to turn to either, that’s also illegal.

  7. Vera

    If people like Rabenek want to lie and say there is any informed consent for any cancer screening in Ontario, they are welcome to do so but it’s not true. You can opt out of invitation letters but will be red flagged as being non compliant by CCO and a troublesome patient so good luck finding a primary care provider. Alberta has a true opt out system, we do not. They were even giving money to doctors to meet cancer screening quotas, informed consent my a.s.s. I was told by the privacy commissioner at CCO that I could not get removed from being red flagged as per Alberta and had no choice in the matter.

  8. Andrey Blitzer

    When I graduated from medical school in 1982, my resident told me that if you got Breast Ca,sooner or later you would die of breast Ca. That is no longer true. Yes, our treatments are better, but I believe the change is also due to earlier detection. Data can be played and manipulated. My clinical experience of 30 years tells me that mammograms are better than our cash strapped health care system is currently painting them.

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