Mammography
An expert on the value of cancer screening tests asks radiologists to stop attacking studies that question the value of screening mammograms. (Rui Vieira / Associated Press)
By Karen Kaplan
Medical Research Breast Cancer Science
When it comes to using mammograms as a tool to screen women for breast cancer, how do you define success? At a minimum, you’d want to know that women who get mammograms are less likely to die of breast cancer than women who didn’t get the tests.
So the big Canadian study published last week in the British Medical Journal was rather inconvenient for the die-hard fans of mammography. The study sorted nearly 90,000 women into two groups. About half of them had mammograms, and the other half didn’t. Those who had the screening tests were more likely to be diagnosed with breast cancer.
You might expect this to be useful, by catching cancers at an earlier, more treatable stage. But it didn’t turn out that way. After tracking these women for up to 25 years, the researchers found that women who had mammograms succumbed to breast cancer at the same rate as women who didn’t get the tests.
The American College of Radiology – the medical group that represents the doctors who read mammograms – pounced on the study right away. In a statement, the ACR called the study “incredibly flawed and misleading.” Taking its results seriously “would place a great many women at increased risk of dying unnecessarily from breast cancer,” it warned.
As my colleague Monte Morin reported, the authors of the study said they stood by their results. But the accusations from high-profile radiologists have kept coming.
Now an expert on preventive medicine and screening is fighting back. In an opinion essay published online Wednesday on CNN.com, Dr. H. Gilbert Welch of the Dartmouth Institute for Health Policy and Clinical Practice explains why the ACR’s two main arguments against the Canadian National Breast Screening Study study are wrong.
First, the radiology group claimed the Canadian results could not be trusted because the women were screened with “second-hand mammography machines” that were operated by technologists who “were not taught proper positioning,” producing sub-par breast films read by radiologists who “had no specific training in mammographic interpretation.”
Welch sums up the ACR critique like this: “Canada is a Third World country.” Not only is this not true, he writes, it’s disingenuous. That’s because the clinical trials that radiologists cite in favor of mammography are even older than the Canadian study. “In fact, one of the trials most favorable to screening – the Health Insurance Plan of New York’s – dates from two decades before Canada’s, in the early 1960s, when mammography technologies were primitive,” Welch writes.
The ACR’s other complaint is that the Canadian trial stacked the odds against mammography by assigning women with “large incurable cancers” to the group that got the mammograms. “This guaranteed more deaths among the screened women than the control women,” according to the ACR statement.
Once again, Welch isn’t buying it. Critics have made this allegation before, and it’s so serious that Canada’s National Cancer Institute initiated a two-year investigation. As reported in the Canadian Medical Assn. Journal in 1997, the investigators “found no evidence of a deliberate attempt to conceal the alterations.”
Nor is there any evidence of cheating in the data, Welch explains. If the Canadian researchers were shunting the sickest patients into the mammogram group, then there were would be more deaths among women who had mammograms than among women who didn’t. But there weren’t. “The rate of death in the two groups was exactly the same, every year, for 25 years,” Welch writes.
Welch has coauthored many studies about mammography, and he says there’s a good explanation for why mammograms don’t seem to be helpful as a screening tool: the tests find “small, unimportant” abnormalities that are labeled “cancer” but are “not destined to cause them any problems,” he writes. (Also, better treatments have erased much of the advantage of finding cancers early.)
Though some radiologists have accepted the growing evidence that screening mammography is flawed, members of the “old guard” are still quick to attack the studies that don’t fit their worldview, Welch writes. He has some advice for those people: Grow up.
“It’s time to stop the unfounded allegations,” Welch writes on CNN. “It might be standard procedure for politics but not for science. Too much energy has been devoted to discrediting the Canadian study and not enough to understanding it.”
Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence.
New England Journal of Medicine, Clinical Article
Bleyer A. and Welch H.G. – To reduce mortality, screening must detect life–threatening disease at an earlier, more curable stage. Effective cancer–screening programs therefore both increase the incidence of cancer detected at an early stage and decrease the incidence of cancer presenting at a late stage. This study examines the Effect of Three Decades of Screening Mammography on Breast–Cancer Incidence. It was concluded that despite substantial increases in the number of cases of early–stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer.
Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer.
Is routine breast cancer screening doing more harm than good?
Public discussion about the risks of over-diagnosis of breast cancer have left some women wondering whether they should take part in the government’s breast screening program. Let’s take a look at what the evidence says and how women might be enabled to make their own decisions about whether to participate…
Public discussion about the risks of over-diagnosis of breast cancer have left some women wondering whether they should take part in the government’s breast screening program.
Let’s take a look at what the evidence says and how women might be enabled to make their own decisions about whether to participate.
Last year Sir Michael Marmot, Professor of Epidemiology and Public Health at University College London, was asked to chair an independent panel to review the benefits and harms of screening mammography in the United Kingdom. The panel focused on the findings from randomised trials, even though most of these trials were carried out a long time ago, in the 1970s and 1980s.
A report on the findings of the review and an accompanying editorial were published in the Lancet late last month. In summary, the report said that screening resulted in an estimated ratio of cases over-diagnosed, to deaths from breast cancer prevented, of 3:1. An over-diagnosed case is one where screening has identified a breast cancer that will never cause harm.
As it is not currently possible to distinguish breast cancer identified through screening which will never cause harm from cancer that will, all breast cancer identified by screening is treated – with surgery and various combinations of radiotherapy, chemotherapy, endocrine and biologic therapies.
A woman treated needlessly will have no way of knowing that her cancer was harmless and that her well-being has been sacrificed, without her knowledge or consent, for the sake of others who may have benefited from screening.
Assessing the benefits of screening
The benefits of screening appear to have been over-estimated.
Advances in treatment have changed the outlook for women with breast cancer so profoundly over the past two decades that the potential for screening to further reduce deaths from breast cancer has been considerably reduced since the original randomised trials were performed.
Furthermore, limiting the estimated benefit to reduced deaths from breast cancer is misleading because radiotherapy after surgery for breast cancer materially increases the risk of dying from heart disease.
The magnitude of overdiagnosis has also been underestimated. An estimate of overdiagnosis from Australia – adjusted for confounders and lead time and assuming 60% of invited women attend – found an over-diagnosis rate of 30% to 40% depending on the expected incidence without screening, rather than the 19% in the Lancet report.
The Nordic Cochrane Center review of screening mammography has estimated the ratio of cases over-diagnosed to deaths from breast cancer prevented at 10:1. Our estimate of the ratio in Australia, using a lower estimate of deaths prevented due to the impact of improved treatment and the higher rate of over-diagnosis, is closer to 15:1.
The clear message is that over-diagnosis exists, it happens regularly as part of the screening process and women need to understand this.
An informed decision
When an asymptomatic woman requests screening mammography through her doctor or when a doctor recommends that an asymptomatic woman be screened, the doctor has a responsibility to inform her about the potential harms and benefits so she can decide whether she will have the mammogram in the context of her situation and preferences.
But when a woman receives an invitation for screening from a government body that makes little or no reference to screening-related harm, she may reasonably expect that that there is no real likelihood of harm. It could be argued that the weight of responsibility for full and frank disclosure of risks and benefits is even greater when the invitation comes from a trusted government agency that has been historically responsible for promoting screening.
It’s time to review the routine invitation for screening to all women aged 50 to 69 years.
The proportion of women in the invited age group who currently attend for screening in Australia is between 50% and 60% so not all women currently respond to the invitation by attending.
Stopping the routine invitation for screening would not prevent women being screened. Women with a high risk of cancer – those with a family or personal history of breast cancer – should still be screened. There may be others who should consider screening because they have a combination of less powerful risk factors which might put them at above average risk.
Other women, not at above-average risk, could request screening if this is what they want.
If women elect not to be screened and only enter the medical system when a clinical problem presents itself, they can be reassured that they will have the benefit of the recent improvements in breast cancer treatment.
Next steps
Government should undertake a review of the invitation for screening. But this will take time.
For the time being, it is imperative that all women be provided with comprehensive information about the disadvantages as well as the advantages of mammographic screening. The pamphlet produced by the Nordic Cochrane Center, which presents the information in terms of the impact of screening on absolute risks and benefits, would make an excellent model.
But a pamphlet alone is insufficient. Given the risks, each woman must be given the opportunity to discuss her options and decide what is best for her, with those who are in a position to provide accurate and helpful advice.
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Recent studies have shown that mammography may do more harm than good. As the issue is still controversial, I recommend women read the evidence carefully as to why some experts have reached this conclusion.
A brief summary of what we know:
The analysis to date of all randomized controlled trials for mammography have concluded there is a marginal benefit.
The reality is that many of the tumors that are found “early” would not have become life-threatening metastatic cancers, and unfortunately, some of the treatments for these “early” cancers themselves have life-threatening side effects. Some aggressive tumors aren’t picked up by mammography, and still others that are may continue to be life-threatening even when found “early”
The United States Preventive Services Task Force no longer recommends Breast self examination (BSE) for women. The National Cancer Institute states that “Based on solid evidence, formal instruction and encouragement to perform BSE leads to more breast biopsies and to the diagnosis of more benign breast lesions” and based on evidence “does not reduce breast cancer mortality.”
About 80% of breast cancers not discovered by mammography are discovered by women themselves, but this is most often a part of daily living- for example, showering or getting dressed- and not part of a systematic, regular BSE.
Using Mammography to screen women with no symptoms is different from having a diagnostic mammogram to evaluate a symptom, such as a lump in the breast or a discharge. The debate is not about whether to perform mammograms on women with symptoms; the mammography controversy is about its efficacy as a screening tool.
An estimated 30% of all breast cancer cases are considered to be over-diagnosed and over-treated. Over-diagnosis, a downside of screening, is diagnosis of cancer that would not have presented within the lifetime of the patient.
For every 2000 women invited for screening over a 10 year period, one will have her life prolonged, and 10 healthy women,who would not have been diagnosed if they had not been screened, will be treated unnecessarily.
In fact, the absolute risk of a woman dying of breast cancer is less than 1% without any screening. Looking at this in another way, 995.6 out of 1,000 50-year-old women will not die of breast cancer within the next 10 years. This number rises to 996 out of 1,000 with regular mammographic screening.
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DO SCREENING MAMMOGRAMS INCREASE YOUR RISK OF BREAST CANCER?
Screening mammography causes net harm
The highly respected Nordic Cochrane Centre have just produced a leaflet with the benefits and harm of screening mammograms.
To summarise:
If 2,000 women are regularly screened for 10 years
* One woman will benefit and will avoid dying from breast cancer
* 200 women will receive false positives
* 10 women will be unnecessarily treated with surgery, radio- and/or chemotherapy, increasing her risks of dying from heart problems and even cancer.
Are they right? Researchers at Southampton University set out to ´assess the claim in the Cochrane report that mammographic breast cancer screening could be doing more harm than good´. The findings, published in the British Medical Journal, December 2011 agreed with Cochrane and stated that mammograms indeed have ´caused net harm´. James Raftery, lead researcher added,”The default is to assume that screening must be good; catching something early must be good, but if a woman has an unnecessary mastectomy, or chemotherapy or radiation, that´s a tragedy. It´s difficult to balance the gain of one life against 200 false positives and 10 unnecessary surgeries”.
Back to Cochrane who say that nowadays with women more ´breast aware´ and with a new generation of diagnostics and treatments, the need for screening mammograms has simply become outdated.
“It therefore no longer seems reasonable to attend for breast cancer screening. In fact, by avoiding going to screening, a woman will LOWER her risk of getting a breast cancer diagnosis.”
Screening mammograms officially still condoned
We are told repeatedly by Cancer Research UK and the NHS that regular screening mammograms, or breast cancer screening, saves lives. But does it really?
Every week it seems more research comes out clearly pointing to increased dangers and risk. Some experts even suggest that screening mammograms can actually cause breast cancer, with the group of women who have a genetic weakness at the highest risk, while others talk about false positives, over diagnosis and of untold worry and mental (not just physical) damage to women who were diagnosed yet simply never had breast cancer in the first place.
Screening is offered to all women in the UK between the ages of 50 and 70 every three years and this is being extended to 43 to 73 years. If you are at ´higher risk´, due to a family history of breast cancer, you may ask to be screened earlier and NICE recommends you are screened every year. As we will see later, this could be very dangerous.
Cancer Research UK are a bit woolly about how many lives are actually saved: ´In 2009, experts looked back at all the results from the screening trials that took place from the 1960s and 1990s. All the results together suggested that breast screening can reduce the number of deaths from breast cancer by about 15 per cent in women who are regularly screened. …. 500 lives saved in the UK each year. But there is still a lot of debate about this. Some scientists think the benefits are much greater at around 1400 lives saved in the UK per year´. But then it adds that another European study, conducted since the 1990s, suggests screening, ´might not save as many lives as we thought´. (Ed: Is that the 1400, or the 500?)
The NHS insists screening saves 1,400 lives a year. ´Not true´, says Professor Peter Gotzsche of Nordic Cochrane Centre in Copenhagen. Writing in the ´Journal of the Royal Society of Medicine´ in August 2011 he states “Information provided to the public by the NHS Breast Screening Programme is seriously misleading, downplays the most important harm, and has remained largely unaffected by repeated criticism and pivotal research questioning the benefits of screening and documenting substantial overdiagnosis. This is unacceptable”. In the Times (September 1st) he adds, “If screening was a drug it would have been withdrawn. You don´t market a drug that harms so many people for such uncertain benefit”.
The Nordic Cochrane centre has reviewed one of the major studies often used to show ´lives saved´ – and concluded that the data was wrong. Indeed, they conclude that there was a higher level of breast cancer in the group screened regularly.
Constant negative research over recent years
Radiation exposure in known to cause genetic mutation in breast cells. It is also known to switch off the tumour suppressing gene (p16). 2011 research from the Lawrence Berkeley National Laboratory in America (a US Government facility) has shown that radiation both changes the environment around breast cells AND increases the risks of mutation within them; a mutation that can be passed on in cell division.
This study showed that 4 to 6 weeks after exposure to radiation at a level below that of a screening mammogram, breast cells started to prematurely age. This resulted in their inability to send certain chemical messages into their immediate environment, which then filled with pre-cancerous mutated cells also from the radiation. ” Our work shows that radiation can change the microenvironment of breast cells, and this in turn can allow the growth of abnormal cells with a long-lived phenotype that have a much greater potential to be cancerous”, said Paul Yaswen, a cell biologist and breast cancer research specialist with Berkeley Lab´s Life Sciences Division, adding “Many in the cancer research community, especially radiologists, have been slow to acknowledge and incorporate in their work the idea that cells are not independent entities, but are highly communicative with each other and with their microenvironment.
The myth of early diagnosis
It is also questionable whether screening mammograms can even provide genuine ´early diagnosis´ as is frequently claimed. A new blood test being developed in America and Nottingham, England will pick up on proteins developed by the very earliest ´rogue´ cells almost before a cancer has formed. In the press release the scientists claim that this is a good 4 years before a mammogram can show up a tumour. Apparently, a cancer makes about 40 divisions during its life, and mammograms cannot pick up a breast tumour until it is of a sufficient size, usually around 20 such divisions. So much for early diagnosis!
Increasing concern
In Spring 2009, nine American scientists were so concerned by what they felt were distinctly dodgy practices at the Federal Drugs Agency, (FDA) they wrote to new President Obama, One of their main causes for concern was the FDA’s silence over the increasing knowledge of the risks associated with mammograms.
These concerns are part of a growing trend. Perhaps one of the most damning reports was a large scale study by Johns Hopkins published in 2008 in the prestigious Journal of the American Medical Association´s Archives of Internal Medicine (Arch Intern Med. 2008;168[21:2302-2303). In the Background to the research it was pointed out that breast cancer diagnosis rates increased significantly in four Scandanavian counties after women there began receiving mammograms every two years. Now, there will be those who will simply argue that this just shows the power of mammograms to find (diagnose) breast cancer. They may well be talking rubbish.
In the study looking at two large scale groups of women in Norway, one having a mammogram every two years for 6 years, the other just at the end, the researchers themselves went on to conclude that they cannot link the increased incidence of breast cancer diagnosis simply to more real cases being detected because the rates among regularly screened women were significantly higher than rates among women of the same age who only received a mammogram at the end of the same six year period.
There are therefore three possible logical conclusions:
- The women in the control group who had a mammogram only at the end of year six somehow had their breast cancers heal themselves – the cancer went away without treatment.
- Not all the women diagnosed with irregularities actually had a problem that became breast cancer
- The more breast cancer screening you have, the more your incidence of breast cancer diagnosis increases.
The research was by no means a small study and compared 119,472 women screened every two years, with an identical group of 109,784 who had none.
The researchers themselves went on to conclude that the findings “provide new insight on what is arguably the major harm associated with mammographic screening, namely, the detection and treatment of cancers that would otherwise regress.”
That in itself is a truly important conclusion – the idea that if you leave a cancer alone (even if it has already had 20 divisions), the body can still heal itself.
But the conclusion that quite simply screening mammograms every two years cause an increase in cancers cannot be dismissed!
Radiation risks – especially to ‘at risk’ women
There have been several warnings on the danger of radiation and mammograms. For example, in a research report (the Lancet Dec 7th 2006) on a ten-year trial involving screening use on pre-menopausal women aged 40-50, funded by the Department of Health and Cancer Research UK, the report ended with the comment that, ‘The findings had to be balanced against possible negative considerations such as an increased radiation exposure which might increase risk later in life’.
The American College of Clinical Thermography concluded in 2005 that ‘a steady stream of experts have been publishing new evidence in peer-reviewed journals in the US relating to the risks inherent in using mammography for breast screening. These findings of increased damage are of no surprise to a growing number of doctors and specialists who have known for years that some of the cancers they have to treat are linked to the accumulative effects of mammographic radiation exposure.
Mammography:
New Book: Mammography Screening—truth, lies and controversy
Posted by medconsumers on March 31, 2012
What happens when a popular cancer screening technology is found to be far more harmful than lifesaving? When the finding becomes clear decades after it was oversold to the public? When a lucrative industry, in terms of equipment, breast biopsies, drugs, etc., has already built around it that is now impossible to dismantle?
One might hope that science would win out. After all, mammography has the distinction of being a cancer screening test with extensive research behind it. In his new book Mammography Screening: Truth, Lies and Controversy (Radcliffe Publishing, London/New York: 2012), physician and research scientist, Peter C. Gøtzsche recounts what it was like to take a hard look at that research and find it didn’t match up with mammography’s sterling reputation.
The near-universal reaction? Shoot the messenger. Vicious attacks came from researchers, policymakers, and physicians. Too often aimed at the man himself rather than his critique. Opinions were fixed—mammography is risk-free and lifesaving. Anyone who disagrees publicly is causing deaths in women who might reconsider and stop having mammograms. The book describes the scientist’s 11-year investigation that uncovered mammography’s considerable harms, though they were “hiding” in plain sight—in the original studies that had long ago established mammography screening as a lifesaver.
Dr. Gøtzsche, director of The Nordic Cochrane Centre, Copenhagen, describes himself as someone who knew little about mammography when, in 1999, he was asked by the Danish Research Council to do an in-depth assessment of all mammography-related research. A statistician and expert in clinical trial design and analysis, Dr. Gøtzsche was the right man for the job. Denmark was considering a national screening program, but first wanted to know more. Bad signs were already showing up in Norway where such a program was underway. Screening decreased breast cancer deaths but, ominously, it hadn’t decreased the rate of deaths from all causes. Even more alarming, mammography failed to detect the most aggressive, deadly form of breast cancer.
Central to Dr. Gøtzsche’s conclusions are the nine randomized clinical trials that included a half million women altogether. The first took place in New York City, in the early 1960s; the last were conducted in Canada and Sweden in the 1980s. “We were baffled by what we found,” he wrote. “We had expected them to be more convincing considering how popular mammography screening had become, despite its high cost.”
The results of these nine trials focused narrowly on mammography screening’s role in reducing breast cancer deaths. Dr. Gøtzsche may well be the first to step back and look at the big research picture, assessing the total death rate and the harm to women. His assessment for the Danish National Board of Health described the benefits as uncertain and raised the possibility that screening could cause more harm than good. It was ignored.
Dr. Gøtzsche continued mining the data from the nine trials and publishing frequently over the next decade. The first paper, co-authored with statistician Ole Olsen, appeared in 2000 in the British journal, The Lancet. But it was their second paper for The Lancet in 2001 that set off a furious international reaction. The nine mammography trials emphasize the number of breast cancer deaths among the participants, but Olsen and Gøtzsche contend that deaths from other causes must also be taken into consideration. These trials show that many more women given regular mammograms are treated for breast cancer than the unscreened women, and these treatments themselves may cause fatalities. Furthermore, overtreatment of ductal carcinoma in situ, often with mastectomy, was identified as “a considerable risk of mammography screening because most cases do not become invasive.” (Disclosure: I serve on The Nordic Cochrane Centre’s advisory board, am quoted in this book, and have reported Dr. Gøtzsche’s work ever since I first came across it in 2000.)
Reactions in the U.S. media were exceptionally virulent and prolonged. It was likely the first time that most physicians as well as the general public heard that some cancers will never cause death or symptoms. But this was not the first high-decibel mammography media controversy. In 1992, when the Canadian trial was published, it was roundly trashed because it came up with an unpopular finding: Mammography screening did not reduce breast cancer deaths, though it increased the number of cancers detected. Dr. Cornelia Baines, co-director of this trial, expected fellow scientists to take a dispassionate look at the finding to see why it differed from that of the earlier trials. Instead, she became the target of numerous attempts to silence and discredit her.
When the mammography controversy surfaced again in the media in 2001, it was the policymakers, the radiologists, and the breast cancer specialists who came down hardest on Olsen and Gotzsche. To accept their conclusions would mean that hundreds of thousands of women worldwide have been treated for a type of breast cancer that would either regress or remain dormant. Who would “dig deep” into that possibility? Certainly not the doctors who for years have been sending their patients for mammograms. And certainly not the radiologists whose income had increased mightily—less from the screening test itself than from the money-making ancillary activities like stereotactic needle biopsies, continuing education courses, magnetic resonance imaging, and biopsy-related patents (click here for one example).
Most women don’t want to hear about mammography’s harms either. Fear of breast cancer sold them on mammography in the first place—without it, there would be no action to take. In the early 1970s when mammography screening was first introduced in the U.S., most American women were not particularly fearful of breast cancer, largely because it was seen as an old woman’s disease. But a multi-national cancer drug maker took care of that “problem” with annual breast cancer awareness campaigns featuring young breast cancer victims. The fear level is kept high for doctors, too, who are frequently reminded that “failure to diagnose breast cancer” is a leading cause of malpractice lawsuits.
Cancer charities take a well-deserved hit in this book for their refusal to admit that screening has a downside. Their misuse of statistics seems calculated to inflate the benefit of cancer screening. Consider the 30% reduction in deaths bandied about in the early years of mammography promotion. This statistic was downgraded recently to 15% by the U.S. Preventive Services Task Force. But both of these are relative risk statistics, which are typically misunderstood by doctors and consumers alike. Most relevant is the absolute effect of screening, not the relative effect, points out Gøtzsche who provides this explanation: ”If 2,000 women are screened regularly for 10 years, 1 woman will avoid dying from breast cancer, and 10 healthy women who would not have been diagnosed without screening, will have breast cancer diagnosed and be treated unnecessarily.”
At the end of last year, the Canadian Medical Association Journal invited Dr. Gøtzsche to write an editorial entitled, “Time to stop mammography screening?” The Canandian Task Force on Preventive Health Care had just issued new guidelines, stating that “women who do not place a high value on a small reduction in breast cancer mortality, and who are concerned with false-positive results on mammography and overdiagnosis, may decline screening. “ Dr. Gøtzsche describes this as “an important step in the right direction, away from the prevailing attitude that a woman who does not undergo screening is irresponsible.”
It’s hard to imagine that this could ever happen here in the U.S.
This book can serve as a guide to physicians and women who want to make their own informed decisions about mammograpy screening, who want an honest in-depth assessment of the research—one that should have given to the public before the introduction of mass screening. A similar “promote the test first, learn the harms later” story has unfolded recently about the PSA screening test for prostate cancer. You just might want to sharpen your critical skills and prepare in advance for the next cancer screening disaster.
Maryann Napoli, Center for Medical Consumers©
More about Dr. Gotzsche’s work:
Free mammography screening leaflet from the Nordic Cochrane Centre It is also available at The Nordic Cochrane Centre website in 13 languages.
Cut your risk of breast cancer—avoid screening mammograms. One-third of all breast cancers found on a mammogram are the forms of breast cancer that would never cause death or symptoms.
Breast cancer death rate has dropped, but not due to mammography Improvements in breast cancer treatments are most likely cause. ’Before and after’ studies conducted in countries that introduced mammography in the 1990s verify what was noticed in Norway in this era: Screening does not detect the most deadly form of breast cancer; it has not reduced the occurrence of advanced cancers.
Poster for the 2002 Cochrane Colloquium U.S. media coverage of the 2001 Lancet paper.
Overdiagnosis of breast cancer after 14 years of mammography screening.
Source
Division of Mental Health, Norwegian Institute of Public Health, Norway. per-henrik.zahl@fhi.no
Abstract
BACKGROUND:
In 2004 we wrote in Tidsskriftet that mammography screening resulted in massive over-diagnosis and over-treatment of breast cancer. Our study was criticized because we had only five years of follow-up time and did not take account of the fact that increased use of hormone replacement therapy could lead to more breast cancer. We have now been screening women for 14 years, and during a period when the use of hormones has fallen by 70 %.
MATERIAL AND METHOD:
Age-specific incidence rates, detection rates and interval rates for breast cancer in the period 1991-2009 have been computed for 40-79 year-old women. Incidence trends have been calculated using Poisson regression.
RESULTS:
The incidence of breast cancer in the age group 40-49 was stable throughout the period, but rose by 50 % in the age group 50-69 years immediately after the start of screening. There was no significant reduction in the incidence of breast cancer in the age group 70-74. The number of new cases of breast cancer in the period increased from around 2000 to 2750. About 300 cases of ductal carcinoma in situ (DCIS) were also diagnosed. Today a total of some 1050 more women have been diagnosed than before screening started. Our calculations indicate that in the absence of screening, around 800 of these women would never have become breast cancer patients.
INTERPRETATION:
The figures from 14 years of mammography screening indicate that all increase in the incidence of breast cancer is due to over-diagnosis: findings of tumours that in the absence of screening would never have given rise to clinical illness.
What are the benefits and harms of attending a screening programme for breast cancer?
How many will benefit from being screened, and how many will be harmed?
What is the scientific evidence for this?
What you always wanted to know about breast screening
Published by The Nordic Cochrane Centre 2012
2. Content.
Summary …………………………………………………………………………… 3
What is screening? ……………………………………………………………… 4
Benefits ………………………………………………………………………….. 4
Harms ……………………………………………………………………………. 5
Documentation for the facts and figures …………………………………. 6
Benefits ………………………………………………………………………….. 7
Harms ……………………………………………………………………………. 9
Why have we written this leaflet? ………………………………………… 10
References ………………………………………………………………………. 13
Written by:
Peter C. Gøtzsche, professor, chief physician, DrMedSci, director, The Nordic Cochrane Centre, Rigshospitalet, Copenhagen, Denmark.
Ole J. Hartling, chief physician, DrMedSci, former chairman, The Ethical Council, Denmark.
Margrethe Nielsen, midwife, MSc, lecturer, Metropolitan University College, Copenhagen, Denmark.
John Brodersen, associate professor, general practitioner, PhD, University of Copenhagen, Denmark.
This leaflet is available at http://www.cochrane.dk and http://www.screening.dk.
January, 2012 (2nd edition; 1stedition published in January 2008)
4. What is screening?
Screening means examining a group of people in order to detect disease or to find people at increased risk of disease.
In many countries, women between 50 and 69 years of age are offered an X-ray examination of the breasts – screening with mammography – every second or third year. The purpose of the screening examination is to find women who have breast cancer in order to offer them earlier treatment.
Screening with mammography has both benefits and harms. The aim of this leaflet is to help each woman weigh up the pros and cons in the light of her own values and preferences, in order that she can make a personal decision whether she wishes to attend.
If nothing abnormal is found by screening, it makes the woman feel reassured that she is healthy. But almost all women feel healthy before they are invited to screening. Furthermore, the invitation itself may cause insecurity. Therefore, screening creates both security and insecurity.
Benefits
Reduced risk of dying from breast cancer – Regular screening with mammography cannot prevent breast cancer, but it can perhaps reduce the risk of dying from breast cancer. A systematic review of the randomised trials of mammography screening found that:
If 2000 women are screened regularly for 10 years, one will benefit from screening, as she will avoid dying from breast cancer because the screening detected the cancer earlier. Since these trials were undertaken, treatment of breast cancer has improved considerably. Women today also seek medical advice much earlier than previously, if they have noted anything unusual in their breasts. In addition, diagnosis and treatment have been centralised in many countries and are now provided by teams of breast cancer experts.
Because of these improvements, screening is less effective today and newer studies suggest that mammography screening is no longer effective in reducing the risk of dying from breast cancer (see Documentation for the facts and figures below).
Screening does not reduce the overall risk of dying, or the overall risk of dying from cancer (including breast cancer
Benefits
The most reliable results come from trials where the women have been randomly assigned to be screened with mammography or not to be screened. About 600,000 healthy women have participated in such trials (5). Half of the trials have been carried out in Sweden. A review of the Swedish trials from 1993 showed that screening reduced breast cancer mortality by 29% (6).
While this appears to be a large effect, here’s what the 29% actually means. The review noted that after 10 years of screening, this reduction in breast cancer mortality corresponded to one woman out of 1000 avoiding dying from breast cancer.
The benefit of screening is thus very small. The reason for this is that in a period of 10 years only 3 women out of 1000 get breast cancer and die from it. The absolute reduction in breast cancer mortality was therefore only 0.1% (1 out of 1000) after 10 years in the Swedish trials. Screening for more than 10 years might increase the benefit, but it will also increase the harms.
The reason why we only describe a period of 10 years is that there are no reliable data for longer time periods.
Another review of the Swedish trials, from 2002, found a reduction in breast cancer mortality of only 15% with one method of calculation, and 20% with another method (7).
The two reviews of the Swedish trials have the shortcoming that the researchers did not take into account that some of the trials had been better done – and therefore are more reliable – than others (5).
The most thorough evaluation of all the randomised trials that exists is a Cochrane review (5). Here, the breast cancer mortality reduction was 10% in the most reliable trials and 25% in the least reliable trials. Since unreliable trials usually overestimate the effect, the reduction was estimated to be 15% (5).
Another thorough evaluation of the trials by independent researchers was carried out on behalf of the U.S. Preventive
Services Task Force. The researchers found a reduction of 16% (8). Hence, these two systematic reviews found an effect on breast cancer mortality that was only half as large as in the first Swedish review from 1993. This means that regular screening of 2000 women for 10 years is necessary to save one of them from dying of breast cancer. The absolute reduction in breast cancer mortality was therefore only 0.05%. Screening does not reduce the overall risk of dying, or the overall risk of dying from cancer (including breast cancer) (5). It therefore seems that women who go to screening do not live longer than women who do not go to screening.
Since the randomised trials were carried out, there have been important advances in diagnosis and treatment. This means that the effect of screening is smaller today. In fact, more recent, rigorous studies suggest that screening is no longer effective (1,9).
In Denmark, for example, screening was introduced in only two regions, corresponding to one fifth of the population. Throughout 17 years, women living in the rest of the country were not offered screening, and very few of these women had a screening mammogram. The annual decline in breast cancer mortality in the age group that could benefit from screening was 1% in the screened areas and 2% in the non-screened areas. In women who were too young to benefit from screening the declines were larger, 5% and 6%, respectively (10). This means that these declines in breast cancer mortality were not caused by screening but by better treatment.
Women below age 50 years are rarely offered screening in Europe. Yet there was a 37% drop in breast cancer mortality between 1989 and 2005 in these women, whereas it was only 21% in women aged 50-69 years (11). The declines began before organised screening in many countries. A comparison of three pairs of neighbouring European countries that had introduced screening 10-15 years apart showed no relation between screening start and the reduction in breast cancer mortality (12). The reduction in breast cancer mortality was about the same in these six European countries as in the United States(13).
An Australian study found that most, if not all, of the reduction in breast cancer mortality could be attributed to improved treatment (hormonal and chemotherapy) (14). Data on stage and size of tumours provide an explanation for these negative findings (1). If screening does not reduce the occurrence of advanced cancers, then it cannot work. A systematic review of studies from seven countries showed that the rate of advanced breast cancers (defined as malignant tumours larger than 20 millimetres) was not affected by screening (15).
Harms
The randomised trials showed that screening increased the number of women who were given a breast cancer diagnosis and were treated by 30%, compared with the women in the group that was not screened (5). This high level of overdiagnosis has also been found in large population studies from European countries, the United States, Canada and Australia. A systematic review of countries with organised screening programmes found 52% overdiagnosis (16). In Denmark, which has a non-screened control group, the overdiagnosis rate was 33% (17). From the Cochrane review (5) it can be calculated what an overdiagnosis of 30% means for women. In the trials from Canada and Malmö, either the whole breast or part of it was removed from 1424 women in the screened group and from 1083 women in the unscreened control group. Since the control group comprised 66,154 women, the overdiagnosis constituted (1424-1083)/66,154 x 2000 = 10 women per 2000 screened women.
Thus, by screening 2000 women, 10 healthy women will receive a cancer diagnosis they would not have had if they had not been screened. They have breast surgery and usually receive other treatments, too, as if they were cancer patients. Without screening, they would have been OK. Studies from the United States, Sweden and Norway suggest that half or more of the screen-detected cancers would have disappeared spontaneously, if they had been left alone, without any treatment at all (18). Most of the earliest cell changes found at screening (carcinoma in situ) are also harmless, as they would never have progressed into invasive cancer (5). The Cochrane review showed that the breast was removed in 20% more women in the screened group than in the control group (5). Other studies have also shown that more women have a breast removed when there is screening than when there is no screening (5). This has been confirmed with data from both the Danish (9) and the Norwegian (19) screening programmes. Furthermore, in the United Kingdom the whole breast was removed in 29% of those cases where the cancerous lesions were detected in very early stages when they had not spread, although those should have been the very cases where a less extensive operation could have been performed (20).
The psychological strain until it is known whether or not there is a cancer, can be severe (5,21). In the United States it has been calculated that after 10 rounds of screening, 49% of healthy women will have experienced a false alarm (22). In Norway, 21% will have experienced a false alarm after 10 rounds of screening (23). However, the numbers for Norway and most other countries are too low because recalls due to poor technical quality of the mammogram have usually not been included (23). As the women are just as affected by such recalls as by a real suspicion of cancer (21), they should be counted as false alarms. In Copenhagen, 13% will have experienced a false alarm after 10 years of screening (5 rounds) (24). Using 10% as an overall estimate for Europe, this corresponds to 200 healthy women for each 2000 women screened for 10 years. As mentioned earlier, about half of women experience pain at mammography when the breasts are squeezed flat. This appears from a systematic review of the relevant studies (25).
Why have we written this leaflet?
In 1999, when considerable doubt had been raised in Denmark about the value of mammography screening, the Danish National Board of Health asked physician and scientist Peter C Gøtzsche from The Nordic Cochrane Centre to assess the mammography screening trials (1). The centre’s report later became extended as a Cochrane review (5), which is the most comprehensive review of the screening trials there is.The Nordic Cochrane Centre is an independent research centre, which has published more research on mammography screening than any other independent institution. In 2006, after we had published a critical review of invitations to screening in several countries, including Denmark (2), the Danish National Board of Health held a meeting asking for suggestions for revisions of the Board’s information leaflet.
The four authors of the leaflet you are currently reading were invited to the meeting. The Danish National Board of Health paid no attention to our comments and published a revised leaflet that we felt contained serious errors (1). We therefore decided to write our own leaflet, which we published in 2008 after having tested it carefully, both among health professionals and lay people.
As the official leaflet being used in the United Kingdom was equally misleading as the one from the Danish National Board of Health, and as those updating it had been similarly resistant to good arguments as the Board, we wrote a paper solely about the shortcomings of the UK leaflet. We published our observations in the British Medical Journal in 2009 together with a translation of our own leaflet (3). The US Center for Medical Consumers called our leaflet “the first honest mammography information for women written by health professionals” (1). We think this is the reason that volunteers have translated it into other languages so that it now exists in 13 languages.
The information women receive when they are invited to attend for screening with mammography is insufficient, one-sided and erroneous (1-3). The letters of invitation emphasize the benefits of screening, but they do not describe how many healthy women will experience the most important harms, overdiagnosis and over treatment. When women are invited to mammography screening, the practice often is that, when they receive a letter about screening, they are also given an appointment time for the examination. This procedure puts pressure on women to attend. Because of this, their participation becomes less voluntary. In some countries, they are even phoned at home and encouraged to attend, which is also potentially coercive.Information on the internet, e.g. on cancer charity web sites,often omits the most important harms. Or they are described as benefits.For example, screening is said to reduce the risk that a woman
loses her breast (1). This is not true. Because of overdiagnosis and overtreatment, screening increases the risk of mastectomy.
We recommend the following websites if you would like further information:
• the National Breast Cancer Coalition
(www.stopbreastcancer.org), whose members are mainly women with breast cancer, and
• the Center for Medical Consumers (www.medicalconsumers.org)
This leaflet provides necessary, basic information about the benefits and harms of screening with mammography to enable a woman – together with her family and her doctor if she wishes – to make a free and informed decision whether to attend for screening.
The leaflet is available at http://www.cochrane.dk and http://www.screening.dk. We welcome comments and criticisms, at general@cochrane.dk.
References
1. Gøtzsche PC. Mammography screening: truth, lies and controversy.
London: Radcliffe Publishing; 2012.
2. Jørgensen KJ, Gøtzsche PC. Content of invitations to publicly funded
screening mammography. BMJ 2006;332:538-41.
3. Gøtzsche P, Hartling OJ, Nielsen M, et al. Breast screening: the facts – or
maybe not. BMJ 2009;338:446-8.
4. Jørgensen KJ, Gøtzsche PC. Presentation on websites of possible benefits
and harms from screening for breast cancer: cross sectional study. BMJ
2004;328:148-51.
5. Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography.
Cochrane Database Syst Rev 2009;4:CD001877 (available at
http://www.cochrane.dk).
6. Nyström L, Rutqvist LE, Wall S, et al. Breast cancer screening with
mammography: overview of Swedish randomised trials. Lancet
1993;341:973–8.
7. Nyström L, Andersson I, Bjurstam N, et al. Long-termeffects
ofmammography screening: updated overview of the Swedish randomised
trials. Lancet 2002;359:909-19.
8. Humphrey LL, Helfand M, Chan BK, et al. Breast cancer screening: a
summary of the evidence for the U.S. Preventive Services Task Force. Annals
of Internal Medicine 2002;137(5 Part 1):347–60.
9. Jørgensen KJ, Keen JD, Gøtzsche PC. Is mammographic screening
justifiable considering its substantial overdiagnosis rate and minor effect on
mortality? Radiology 2011;260:621-6.
10. Jørgensen KJ, Zahl PH, Gøtzsche PC. Breast cancer mortality in
organised mammography screening in Denmark: comparative study. BMJ
2010;340:c1241.
11. Autier P, Boniol M, La Vecchia C, et al. Disparities in breast cancer
mortality trends between 30 European countries: retrospective trend analysis
of WHO mortality database. BMJ 2010;341:c3620.
12. Autier P, Boniol M, Gavin A, et al. Breast cancer mortality in neighbouring
European countries with different levels of screening but similar access to
treatment: trend analysis of WHO mortality database. BMJ 2011;343:d4411.
13. Bleyer A. US breast cancer mortality is consistent with European data.
BMJ 2011;343:d5630.
14
14. Burton RC, Bell RJ, Thiagarajah G, et al. Adjuvant therapy, not
mammographic screening, accounts for most of the observed breast cancer
specifi c mortality reductions in Australian women since the national screening
program began in 1991. Breast Cancer Res Treat. Epub 2011 Sep 29.
15. Autier P, Boniol M, Middleton R, et al. Advanced breast cancer incidence
following population based mammographic screening. Ann Oncol 2011;20 Jan
[Epub ahead of print].
16. Jørgensen KJ, Gøtzsche PC. Overdiagnosis in publicly organised
mammography screening programmes: systematic review of incidence trends.
BMJ 2009;339:b2587.
17. Jørgensen KJ, Zahl P-H, Gøtzsche PC. Overdiagnosis in organised
mammography screening in Denmark: a comparative study. BMC Women’s
Health 2009;9:36.
18. Zahl PH, Gøtzsche PC, Mæhlen J. Natural history of breast cancers
detected in the Swedish mammography screening program; a cohort study.
Lancet Oncol 2011 Oct 11 [Epub ahead of print].
19. Suhrke P, Mæhlen J, Schlichting E, et al. Effect of mammography
screening on surgical treatment for breast cancer in Norway: comparative
analysis of cancer registry data. BMJ 2011;343:d4692.
20. NHS cancer screening programmes. BASO Breast Audit 1999/2000.
http://www.cancerscreening.nhs.uk/breastscreen/publications.html (accessed Dec
12, 2001).
21. Brodersen J. Measuring psychosocial consequences of false-positive
screening results – breast cancer as an example (ph.d.-afhandling).
Department of General Practice, Institute of Public Health, Faculty of Health
Sciences, University of Copenhagen. Månedsskrift for Praktisk Lægegerning
2006 (ISBN 87-88638-36-7).
22. Elmore JG, Barton MB, Moceri VM, et al. Ten-year risk of false positive
screening mammograms and clinical breast examinations. N Engl J Med
1998;338:1089–96.
23. Hofvind S, Thoresen S, Tretli S. The cumulative risk of a false-positive
recall in the Norwegian Breast Cancer Screening Program. Cancer
2004;101:1501-7.
24. Njor SH, Olsen AH, Schwartz W, et al. Predicting the risk of a falsepositive
test for women following a mammography screening programme. J
Med Screen 2007;14:94-7.
15
25. Armstrong K, Moye E, Williams S, et al. Screening mammography in
women 40 to 49 years of age: a systematic review for the American College of
Physicians. Ann Intern Med 2007;146:516-26.
Other relevant literature
Welch H. Should I be tested for cancer? Maybe not and here’s why. Berkeley:
University of California Press; 2004.
Vainio H, Bianchini F. IARC Handbooks of Cancer Prevention. Vol 7: Breast
Cancer Screening. Lyon: IARC Press, 2002.
Further information can be obtained by contacting the doctor
ead the latest information from the Cochrane centre, a highly rated independent and non-profit making organization.
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Is your life saved by Mammography. read this: http://www.ncbi.nlm.nih.gov/pubmed/2202509
Estimates of overdiagnosis of invasive breast cancer associated with screening mammography:
http://www.ncbi.nlm.nih.gov/pubmed/19894130
http://www.ncbi.nlm.nih.gov/pubmed/21709144
What is the point: will screening mammography save my life?:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2670293/?tool=pubmed
Does breast cancer screening increase the risk of breast cancer:
http://www.canceractive.com/cancer-active-page-link.aspx?n=1420
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An important part of this debate:
Likelihood that a woman with screen-detected breast cancer has had her “life saved” by that screening.
Source
Dartmouth Institute for Health Policy and Clinical Practice, Dartmouth College, Hanover, New Hampshire, USA. H.Gilbert.Welch@dartmouth.edu
Abstract
BACKGROUND:
Perhaps the most persuasive messages promoting screening mammography come from women who argue that the test “saved my life.” Because other possibilities exist, we sought to determine how often lives were actually saved by mammography screening.
METHODS:
We created a simple method to estimate the probability that a woman with screen-detected breast cancer has had her life saved because of screening. We used DevCan, the National Cancer Institute’s software for analyzing Surveillance Epidemiology and End Results (SEER) data, to estimate the 10-year risk of diagnosis and the 20-year risk of death–a time horizon long enough to capture the downstream benefits of screening. Using a range of estimates on the ability of screening mammography to reduce breast cancer mortality (relative risk reduction [RRR], 5%-25%), we estimated the risk of dying from breast cancer in the presence and absence of mammography in women of various ages (ages 40, 50, 60, and 70 years).
RESULTS:
We found that for a 50-year-old woman, the estimated risk of having a screen-detected breast cancer in the next 10 years is 1910 per 100,000. Her observed 20-year risk of breast cancer death is 990 per 100,000. Assuming that mammography has already reduced this risk by 20%, the risk of death in the absence of screening would be 1240 per 100,000, which suggests that the mortality benefit accrued to 250 per 100,000. Thus, the probability that a woman with screen-detected breast cancer avoids a breast cancer death because of mammography is 13% (250/1910). This number falls to 3% if screening mammography reduces breast cancer mortality by 5%. Similar analyses of women of different ages all yield probability estimates below 25%.
CONCLUSIONS:
Most women with screen-detected breast cancer have not had their life saved by screening. They are instead either diagnosed early (with no effect on their mortality) or overdiagnosed.
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However, the Canadian’s have a slightly different set of recommendations: Note weak recommendation for Mammograms (Weak evidence)
CMAJ. 2011 November 22; 183(17): 1991–2001.
Summary of recommendations for clinicians and policy-makers
Recommendations are presented for the use of mammography, magnetic resonance imaging (MRI), breast self-examination and clinical breast examination to screen for breast cancer (see Box 1). These recommendations apply only to women at average risk of breast cancer aged 40 –74 years. They do not apply to women at higher risk because of personal history of breast cancer, history of breast cancer in first-degree relatives, known mutations of the BRCA1/BRCA2 genes or previous exposure of the chest wall to radiation. No recommendations are made for women aged 75 years and older, given the lack of data available for this group.
Mammography
-
For women aged 40–49 years, we recommend not routinely screening with mammography. (Weak recommendation; moderate-quality evidence)
-
For women aged 50–69 years, we recommend routinely screening with mammography every two to three years. (Weak recommendation; moderate-quality evidence)
-
For women aged 70–74 years, we recommend routinely screening with mammography every two to three years. (Weak recommendation; low-quality evidence)
Magnetic resonance imaging
-
We recommend not routinely screening with MRI scans. (Weak recommendation; no evidence)
Clinical breast examination
-
We recommend not routinely performing clinical breast examinations alone or in conjunction with mammography to screen for breast cancer. (Weak recommendation; low-quality evidence)
Breast self-examination
-
We recommend not advising women to routinely practice breast self-examination. (Weak recommendation; moderate-quality evidence)
Conclusion
Although screening mammography reduces mortality from breast cancer among women aged 40–74 years, the absolute benefit is small — especially for younger women — and is partially offset by harms caused by unnecessary intervention. Despite its potential to reduce mortality, appropriate use of mammography will require thoughtful discussion between clinicians and patients about the balance between benefits and harms. Finally, available evidence does not support the use of MRI scans, clinical breast examination or breast self-examination to screen for breast cancer among women at average risk.
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Overdiagnosis of invasive breast cancer due to mammography screening: results from the Norwegian screening program.
Source
Harvard School of Public Health, Brigham and Women’s Hospital, Boston, Massachusetts, USA. mkalager@hsph.harvard.edu
Abstract
BACKGROUND:
Precise quantification of overdiagnosis of breast cancer (defined as the percentage of cases of cancer that would not have become clinically apparent in a woman’s lifetime without screening) due to mammography screening has been hampered by lack of valid comparison groups that identify incidence trends attributable to screening versus those due to temporal trends in incidence.
OBJECTIVE:
To estimate the percentage of overdiagnosis of breast cancer attributable to mammography screening.
DESIGN:
Comparison of invasive breast cancer incidence with and without screening.
SETTING:
A nationwide mammography screening program in Norway (inviting women aged 50 to 69 years), gradually implemented from 1996 to 2005.
PARTICIPANTS:
The Norwegian female population.
MEASUREMENTS:
Concomitant incidence of invasive breast cancer from 1996 to 2005 in counties where the screening program was implemented compared with that in counties where the program was not yet implemented. To adjust for changes in temporal trends in breast cancer incidence, incidence rates during the preceding decade were also examined. The percentage of overdiagnosis was calculated by accounting for the expected decrease in incidence following cessation of screening after age 69 years (approach 1) and by comparing incidence in the current screening group with incidence among women 2 and 5 years older in the historical screening groups, accounting for average lead time (approach 2).
RESULTS:
A total of 39,888 patients with invasive breast cancer were included, 7793 of whom were diagnosed after the screening program started. The estimated rate of overdiagnosis attributable to the program was 18% to 25% (P < 0.001) for approach 1 and 15% to 20% (P < 0.001) for approach 2. Thus, 15% to 25% of cases of cancer are overdiagnosed, translating to 6 to 10 women overdiagnosed for every 2500 women invited.
LIMITATION:
The study was registry-based.
CONCLUSION:
Mammography screening entails a substantial amount of overdiagnosis.
PRIMARY FUNDING SOURCE:
Norwegian Research Council and Frontier Science.
Comment in
Summary for patients in
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Estimates of overdiagnosis of invasive breast cancer associated with screening mammography.
Source
School of Public Health, University of Sydney, Sydney, NSW, Australia. stephenm@health.usyd.edu.au
Abstract
PURPOSE:
To estimate the extent of overdiagnosis of invasive breast cancer associated with screening in New South Wales, Australia, a population with a well-established mammography screening program which has achieved full geographic coverage.
METHODS:
We calculated overdiagnosis as the observed annual incidence of invasive breast cancer in NSW in 1999-2001 (a screened population) minus the expected annual incidence in this population at the same time, as a percentage of the expected incidence. We estimated expected incidence without screening in 1999-2001 from the incidence of invasive breast cancer in: (1) women in unscreened age groups (interpolation method); and (2) women in all age groups prior to the implementation of screening (extrapolation method). We then adjusted these estimates for trends in major risk factors for breast cancer that may have coincided with the introduction of mammography screening: increasing obesity, use of hormone replacement therapy (HRT) and nulliparity. Finally, we adjusted for lead time to produce estimates of expected incidence in 1999-2001. These were compared with the observed incidence in 1999-2001 to calculate overdiagnosis of breast cancer associated with screening.
RESULTS:
Overdiagnosis of invasive breast cancer among 50-69 year NSW women was estimated to be 42 and 30% using the interpolation and extrapolation methods, respectively.
CONCLUSION:
Overdiagnosis of invasive breast cancer attributable to mammography screening appears to be substantial. Our estimates are similar to recent estimates from other screening programmes. Overdiagnosis merits greater attention in research and in clinical and public health policy making.
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My Comment: This is a very important debate that needs to be had. Women must be fully informed about both sides of the argument, and not just pushed into having mammograms being unaware of the information provided above. If you would like to enter this debate, feel free to comment below.
A Systematic Assessment of Benefits and Risks to Guide Breast Cancer Screening Decisions FREE
ABSTRACT
Importance Breast cancer is the second leading cause of cancer deaths among US women. Mammography screening may be associated with reduced breast cancer mortality but can also cause harm. Guidelines recommend individualizing screening decisions, particularly for younger women.
Objectives We reviewed the evidence on the mortality benefit and chief harms of mammography screening and what is known about how to individualize mammography screening decisions, including communicating risks and benefits to patients.
Evidence Acquisition We searched MEDLINE from 1960-2014 to describe (1) benefits of mammography, (2) harms of mammography, and (3) individualizing screening decisions and promoting informed decision making. We also manually searched reference lists of key articles retrieved, selected reviews, meta-analyses, and practice recommendations. We rated the level of evidence using the American Heart Association guidelines.
Results Mammography screening is associated with a 19% overall reduction of breast cancer mortality (approximately 15% for women in their 40s and 32% for women in their 60s). For a 40- or 50-year-old woman undergoing 10 years of annual mammograms, the cumulative risk of a false-positive result is about 61%. About 19% of the cancers diagnosed during that 10-year period would not have become clinically apparent without screening (overdiagnosis), although there is uncertainty about this estimate. The net benefit of screening depends greatly on baseline breast cancer risk, which should be incorporated into screening decisions. Decision aids have the potential to help patients integrate information about risks and benefits with their own values and priorities, although they are not yet widely available for use in clinical practice.
Conclusions and Relevance To maximize the benefit of mammography screening, decisions should be individualized based on patients’ risk profiles and preferences. Risk models and decision aids are useful tools, but more research is needed to optimize these and to further quantify overdiagnosis. Research should also explore other breast cancer screening strategies.
Breast cancer is the most common noncutaneous cancer and the second leading cause of cancer death among women in the United States. About 40 000 women die of breast cancer in the United States each year.1 For decades, there has been strong interest in screening strategies that will detect early cancers before they progress, thereby reducing mortality. Some trials have demonstrated that mammography is associated with decreased breast cancer mortality, but these data and increasing evidence about the harms of mammography screening have generated controversy. In 2009, in light of evidence that the benefit-risk ratio is higher among women older than 50 years and with less frequent screening, the US Preventive Services Task Force (USPSTF) reversed its previous recommendation of mammography every 1 to 2 years beginning at age 40 years and recommended routine screening every 2 years starting at age 50.2 This was consistent with recommendations in many European countries3,4 but contrasted with several other US organizations,5,6 revitalizing the recurring debate in both the medical community and mainstream media about mammography policy and practice. Recent evidence suggests that use of mammography in the United States has not changed following the USPSTF 2009 recommendations.7
The USPSTF stated that “the decision to start regular, biennial screening mammography before the age of 50 years should be an individual one and take into account patient context, including the patient’s values regarding specific benefits and harms.”2The central issue for clinicians, which is infrequently addressed in the medical literature, is how to individualize mammography recommendations and foster informed decisions by patients. To accomplish this, clinicians must assess a patient’s individual risk for breast cancer, effectively communicate the risks and benefits of screening, identify how a patient’s characteristics might modify those risks and benefits, and elicit patients’ personal preferences and values. This review will address the following key clinical questions: (1) What is the benefit of mammography screening, and how does that vary by age and patient risk? (2) What are the harms of mammography screening? (3) What is known about how to incorporate individual characteristics into breast cancer screening recommendations? (4) How can patients be supported in making informed decisions about mammography screening?
METHODS
We searched MEDLINE for relevant randomized clinical trials (RCTs), meta-analyses, systematic reviews, and observational studies from 1960 to January 19, 2014 (search terms are reported in the eBox in Supplement). We also manually searched the references of key articles, reviews, meta-analyses, and practice recommendations. For describing the breast cancer mortality benefit of mammography we included meta-analyses of RCTs of mammography screening examining breast cancer mortality. From 525 articles identified, 20 meta-analyses met these criteria. We focused on the 5 meta-analyses published after 2006, when the most recent RCT, the Age Trial,8 was published (eFigure 1 in Supplement).
To describe mammography’s harms we focused on false-positive results, unnecessary biopsies, and overdiagnosis, conducting 2 separate searches. The first included systematic reviews and meta-analyses through December 2008, the period for the review informing the 2009 USPSTF decision.9 The second included primary studies and reviews published since December 2008. We identified 374 articles, including 14 systematic reviews or meta-analyses published before 2008 and 72 studies or reviews published after 2008 (eFigures 2 and 3 in Supplement).
For studies on (1) individualizing information about risks and benefits and (2) communicating the benefits and risks to patients considering mammography screening, we searched for interventions (including decision aids) providing probabilistic information to women on the benefits and risks of screening, their own individual breast cancer risk, or both. We did not include interventions designed to increase screening rates without considering screening risks or a woman’s baseline breast cancer risk. From 907 citations, we identified 23 studies (eFigure 4 in Supplement). From MEDLINE searches and reviews of citations, we additionally identified 25 articles on breast cancer risk models and using risk profiles to guide mammography decisions.
In Table 1, we provide summary risk ratios and number needed to invite (NNI) to screening from Nelson et al’s meta-analysis conducted for the USPSTF.9 We also report absolute risk ratios calculated by inverting the NNI.9 In Table 2, we report estimated benefits and harms of breast cancer screening for 10 000 women undergoing annual mammography during a 10-year period. To estimate the number of women diagnosed with invasive breast cancer or ductal carcinoma in situ (DCIS) (column 1), we used Surveillance, Epidemiology, and End Results (SEER) estimates from a recent review by Welch and Passow.16,17 The numbers of breast cancer deaths over 15 years (column 2) use Welch and Passow’s estimates of the 15-year risks of dying of breast cancer in a screened population. The lower number reflects a minimal breast cancer mortality reduction of 5% based on RCTs reporting no benefit,10,15 and the upper number reflects a reduction of 36% based on the trial reporting the highest benefit.11 Column 3 provides Welch and Passow’s upper and lower estimates of the number of deaths averted through screening, based on the same range of RCT results. To estimate the number of invasive breast cancers or DCIS diagnosed that would never become clinically important (overdiagnosis, column 4), we report absolute numbers calculated by Welch and Passow based on the Malmö trial and an epidemiologic study.17,20,21 To estimate the number of women with at least 1 false-positive mammogram or unnecessary biopsy (columns 5 and 6), we report the cumulative incidence (with 95% CIs) from 2 studies using Breast Cancer Surveillance Consortium data22,23 multiplied by 10 000.
Benefits of Screening Mammography
Between the 1960s and the 1990s, 8 large RCTs assessed breast cancer mortality associated with screening. Meta-analyses of these trials generally demonstrate a 15% to 20% decrease in the relative risk of breast cancer–specific mortality. The variation in estimates is largely attributable to differences in trial quality and inclusion criteria. The Edinburgh trial has been most consistently excluded because of concerns about its cluster randomization strategy.24 However in other trials, concerns have been raised about randomization, contamination, and assignment of breast cancer mortality.25
In addition, some argue that the RCTs are unlikely to be applicable to women undergoing screening today, because they preceded treatment advances that have powerfully influenced breast cancer mortality and used older mammography techniques.17 However, the RCTs nevertheless provide the best data available.
Two recent meta-analyses examined breast cancer mortality across all age groups.25,26 The summary risk ratio (RR) for breast cancer mortality reduction with mammography screening at median 11.4 years follow-up was 0.81 (95% CI, 0.74-0.88) in the meta-analysis for the Canadian Task Force that included all RCTs except the Edinburgh trial.26 The Cochrane reviewers reported a summary RR of 0.90 (95% CI, 0.79-1.02) when including only the 3 trials they considered of adequate quality.25 When the Cochrane reviewers included all the trials except Edinburgh, with 13 years of follow-up, their results were consistent with the Canadian review (RR, 0.81 [0.74-0.87]).25 In February 2014, 25-year follow-up results from 2 Canadian trials were published,27 showing no mortality benefit from mammography screening (hazard ratio, 1.05 [95% CI, 0.88-1.12]). These results are consistent with earlier reports from these trials (at 13 years’ follow-up, the mortality rate ratio for women aged 50-59 years was 1.02 [95% CI, 0.78-1.33]15 and at 11-16 years’ follow-up among women aged 40-49 years, it was 0.97 [95% CI, 0.74-1.27]10) and would be unlikely to substantially change meta-analysis results.
Three meta-analyses assessed mortality reduction within multiple age groups,9,25,26 and 2 focused on women aged 40 to 49 years only.28,29 For women aged 40 to 49 years, these 5 meta-analyses provided summary RRs ranging from 0.81 to 0.85. Variation in the estimated RRs again resulted from differing decisions about trial quality and inclusion. In 3 analyses excluding the Edinburgh trial alone, summary RRs for women aged 40 to 49 years were 0.84 (95% CI, 0.75-0.96)9,26 and 0.84 (95% CI, 0.73-0.96).25Table 1 shows estimates from the meta-analysis conducted for the USPSTF.9
Despite similar relative benefits across age groups, because baseline breast cancer risk varies, the absolute benefit and NNI to screening to prevent 1 breast cancer death vary by age (Table 1). Based on the meta-analysis by Nelson et al,9 about 1904 women aged 39 to 49 would need to be invited to prevent 1 breast cancer death, vs 377 women aged 60 to 69. To address the “psychological magnification” of relative risks and most patients’ limited numeracy, experts recommend using natural frequencies (eg, the number of cancers diagnosed among a certain number screened) to aid comprehension of such findings.30,31Table 2 provides published estimates from Welch and Passow of mammography’s benefits using natural frequencies. Welch and Passow provide a range for number of breast cancer deaths in a screened population using results from RCTs with markedly contrasting results—the Canadian trials, which showed no significant breast cancer mortality benefit (Welch and Passow use a more conservative estimate of 5%)10,15 and the Swedish 2-County trial, which showed about a 36% risk reduction among those attending screening.11 Welch and Passow calculated these numbers based on SEER 15-year breast cancer mortality rates18 (assuming that the benefit of mammography would extend beyond the screening period) and adjusted for self-reported mammography rates in the United States,19 providing a range to reflect the uncertainty about the benefit. Based on these estimates, among 10 000 women aged 50 years undergoing annual screening for 10 years, approximately 302 would be diagnosed with invasive breast cancer or DCIS, between 56 and 64 women would die of breast cancer despite screening, and between 3 and 32 breast cancer deaths would be averted through screening depending on the true effect of mammography. Some might argue that the ranges overemphasize extreme RCT results (concerns have been raised about suboptimal randomization in the Swedish trial25) and may be difficult to communicate to patients, and that meta-analyses can at least provide a “best estimate.” If Welch and Passow’s methodology is used but Nelson et al’s9 meta-analysis results are applied to the adjusted SEER breast cancer death rates, among 10 000 women aged 40 years undergoing annual mammography for 10 years, 31 deaths would occur despite screening and 5 deaths would be averted; among 50-year-olds, 62 deaths would occur despite screening and 10 would be averted; and among 60-year-olds, 88 deaths would occur despite screening and 42 would be averted.
Harms of Screening Mammography
False-Positive Results
False-positive results raise suspicion for breast cancer and lead to further testing, such as additional imaging or biopsy, but do not result in a cancer diagnosis.32 Recent evidence from the Breast Cancer Surveillance Consortium suggests that the 10-year cumulative risk of at least 1 false-positive result is 61.3% for women starting screening at ages 40 or 50 years and 49.7% for women aged 66 to 74 years undergoing annual screening.22,23Table 2 shows that among 10 000 women aged 50 years undergoing annual mammography for 10 years, approximately 6130 (95% CI, 5800-6470) will have at least 1 false-positive result.
The risk of false-positive results increases when screening starts at younger ages or occurs annually, leading to more mammograms32,33; this was a key consideration influencing the USPSTF recommendation to pursue biennial screening starting at age 50.2 The significance of a false-positive result for an individual woman, however, is debated, and likely varies substantially by patient. A review of 23 observational studies concluded that false-positive mammography results increase anxiety and distress related to mammography and breast cancer but do not increase clinically diagnosed anxiety and depression.34 There are conflicting data regarding the persistence of anxiety or depressive symptoms over time,35– 38 and whether women are more or less likely to return for subsequent mammograms after a false-positive finding.34,39– 42 About 7.0% to 9.8% of women experience unnecessary biopsies after 10 years of annual screening22,23—approximately 940 (95% CI, 740-1150) of the 10 000 women aged 50 years undergoing annual mammography reported in Table 2.
Overdiagnosis
Overdiagnosis is the detection of a tumor through screening that would not have become clinically evident in the absence of screening. Overdiagnosis can occur either because of a tumor’s indolent pathological features or because of competing mortality risks attributable to older age or comorbidities.43 Previously overdiagnosis was considered primarily explained by DCIS, but it is now thought that some invasive cancer diagnoses also represent overdiagnosis; both types of cases are generally included in analyses, since both are treated. Treatment of an overdiagnosed cancer subjects a patient to the harms of treatment without benefits, since the tumor would not have caused problems if undetected.43
There has been a sharp recent increase in studies examining overdiagnosis, and many authors now describe overdiagnosis as the most concerning potential harm of mammography screening.44 However, substantial uncertainty exists around its magnitude. To measure overdiagnosis, ideally one would compare the number of cancers diagnosed in screened vs unscreened women with the same underlying risk factors and representing the same historical period and region, from the onset of screening until death.43 Adequate follow-up time is needed to account for the lead time gained by screening and to avoid counting cancers detected early through screening as “excess,” or overdiagnosed, cancers.43 Long-term follow up of RCTs comparing screened with unscreened women minimizes these concerns, providing the best estimates of overdiagnosis.45 Three RCTs, the Malmö trial and the 2 Canadian trials, never invited their control groups to screening,10,15,20 allowing assessment of excess cancer incidence in the screened group 6 to 15 years after screening ended. A meta-analysis of overdiagnosis estimates from these 3 trials estimated that among women invited to screen, 19% of all cancers diagnosed during the screening period (and 11% during the entire observation period) were overdiagnosed.44,46 This proportion represents the excess incidence of cancers detected in the screened group over long-term follow-up, as a fraction of all cancers diagnosed in the screened group during the screening period (or the entire observation period).
The RCT findings have limitations, including possible underestimation of overdiagnosis because some screening occurred in the control groups (in the Canadian National Breast Screening Study 1, 26.3% of the control group had at least 1 mammogram outside the study).10,47 Overestimation is also possible since women were not followed up until all had died, although in the recent update of the Canadian trials, excess cases still represented 22% of screening-detected cancers.27,45 The applicability of the RCTs to women undergoing mammography screening today in the United States is also uncertain.17 Because the Malmö trial screened women only every 18 to 24 months and used older, less sensitive mammography techniques, Welch and Passow used the Malmö estimate as a “lower bound” estimate of overdiagnosis risk.17
Published estimates of overdiagnosis from observational studies vary from less than 5% to more than 50%43,48– 50 because of differing populations, assumptions, and measurement methods.43 To identify incidence rates in the absence of screening, observational studies often use historical incidence rates or incidence in an unscreened geographical region. A recent study based on SEER incidence and survival trends using historical incidence rates as a comparison reported that 31% of all breast cancers diagnosed in the United States represented overdiagnosis.21 Welch and Passow used these data as their “upper bound” estimate of overdiagnosis risk.17 In Table 2, we include Welch and Passow’s lower and upper bound estimates to convey the uncertainty and methodological limitations around measuring overdiagnosis17; the estimate from the meta-analysis of 3 RCTs (19%)44 lies between these extremes. It is thus likely that among 10 000 women aged 50 years undergoing annual mammography for 10 years, of 302 cases of cancer or DCIS, between 30 and 137 would reflect overdiagnosis, with a best guess being 57 based on the meta-analysis estimate of 19%.
Individualizing Mammography Screening Decisions
For a woman in the United States, the average lifetime risk of breast cancer is about 12.3%; the 10-year risks of invasive breast cancer at ages 40, 50, and 60 years are 1.5%, 2.3%, and 3.5% respectively.1 Numerous risk factors have been identified for breast cancer, although up to 60% of breast cancers occur in the absence of known risk factors.51 Each individual risk factor confers only a modest relative risk increase, and most are common in the general population; therefore, combinations of risk factors are most frequently used in efforts to estimate breast cancer risk.52 Several risk models attempt to use these risk factors to predict both breast cancer incidence in populations and individuals’ absolute risk. The Gail model, developed in a population of women undergoing annual screening and including age at menarche, age at first birth, number of first-degree relatives with breast cancer, number of previous breast biopsies, and presence of atypical hyperplasia as risk factors, was one of the first.53,54 Several limitations of the Gail model have been described, including its omission of breast density and its limited applicability in certain racial/ethnic groups and high-risk populations.51,55,56 Revisions of the model include more diverse populations57 and breast density,56,58,59 which is associated with a 1.5- to 2-fold increased risk of breast cancer among women aged 40 to 50 years60 but raises the challenging question of whether a baseline mammogram should be obtained in all women. Although these models help refine understanding of a woman’s absolute risk for breast cancer and can help communicate risk to women, they are more accurate in predicting incidence in population subgroups and far less useful in identifying which individual women will or will not get cancer.52,55 Despite its limitations, the Gail model has been validated in 3 large populations and, as the basis for the National Cancer Institute’s online Breast Cancer Risk Assessment Tool (http://www.cancer.gov/bcrisktool), is commonly used in clinical practice.
Several decision analysis models have attempted to estimate how individual risk profiles influence the benefits and harms of screening.61– 63 Older age and other factors that increase breast cancer risk also increase the absolute breast cancer mortality benefit with mammography. The risk of false-positive results also generally increases with certain individual characteristics such as breast density.22,64 Older age and more comorbidity increase the risk of overdiagnosis because of decreasing life expectancy,33 as do characteristics of the cancer itself (aggressive tumors are less likely overdiagnosed than indolent tumors because of shorter lead time). A comparative study of 4 microsimulation models found that for women aged 40 to 49 years with a Gail-model breast cancer risk twice average, biennial mammography screening yielded the same ratio of benefits and harms as biennial screening for women 50 years or older at average risk.63 Similarly, a cost-utility model found that biennial screening among women aged 40 to 49 years with high breast density and either a first-degree relative with breast cancer or a history of a breast biopsy had similar ratios of benefits to harms as biennial screening of women in their 50s without those risk factors.61 Of note, however, none of these models considered overdiagnosis in their main analysis.61,63
If a healthy 40-year-old woman had twice the average risk of breast cancer because of dense breasts, she would be expected to have twice the absolute benefit of annual screening (eg, 10 lives saved per 10 000 instead of 5) (Table 2). She would, however, also have a higher risk of false-positive findings.22
Supporting Informed Decision-Making
Decisions about mammography should involve discussion of risks, benefits, uncertainties, alternatives, and patient preferences.65,66 Although numerous interventions have aimed to increase mammography uptake, including interventions tailored to individuals’ psychological readiness to adopt screening or to individuals’ own risk profiles,67– 75 fewer studies examine measures of an informed decision as an outcome. A Cochrane review of RCTs examined the effects of personalized risk communication on informed decision making about screening for a range of diseases.76 Eighteen studies focused on mammography screening; those assessing outcomes related to informed decisions generally showed an increase in knowledge, quality of life, and accuracy of risk perception with personalized risk communication. Notably, meta-analysis of 4 studies of interventions providing women with numerical information about their risk showed that among women 40 years or older, there was no association between provision of numerical information and uptake of mammography (odds ratio, 0.84 [95% CI, 0.68-1.03]).76
Informed decisions require reconciling information about the risks and benefits of screening with a patient’s values. Decision aids using pamphlets, videos, or Internet tools can provide information, elicit preferences, and help patients make decisions. A Cochrane review77 defined decision aids as “interventions designed to help people make specific and deliberative choices… by providing (at the minimum) information on the options and outcomes relevant to a person’s health status,” and helping patients “to clarify… the value they place on the benefits, harms, and scientific uncertainties.” Overall, decision aids increased knowledge, decreased decisional conflict and anxiety, and had variable effect on uptake of the test or treatment in question. The review’s only mammography study recruited 70-year-old Australian women nearing the upper age cutoff for screening.78 Exposure to the decision aid led to less indecision about continuing mammography, although there was no difference in screening participation the next month. A more recent study among US women 75 years or older administered a paper decision aid just before a primary care encounter. Women who received the decision aid reported knowing more about benefits and risks and screening, decreased intentions to be screened, and were less likely to undergo mammography in the following 2 years.79 One RCT since the Cochrane review examined an online decision aid among women aged 38 to 45 years.80 The decision aid summarized the risks and benefits of mammography and provided a values clarification worksheet. Compared with controls, women who used the decision aid were more knowledgeable and were less likely to report that they would initiate screening now.80
DISCUSSION
Evidence suggests that mammography screening is associated with reduced breast cancer mortality, but the benefit is modest. Although better data are needed to estimate the magnitude of overdiagnosis, the risks of mammography screening are significant, decreasing the net benefit of screening. The net benefit is less for younger women, who have a lower absolute risk of breast cancer and greater risk of false-positive findings, and with annual screening, which increases false-positive findings and would also be expected to increase overdiagnosis.33
Table 3 includes current guidelines from the United States, Canada, and Europe. Despite offering clinicians and patients a general framework for evidence-based decisions, because of their limited incorporation of individual risk profiles other than age, variation across guidelines, and inherent population-based approaches, they have limited utility for guiding patient counseling and decisions. Because risk factors other than age influence the net benefit of screening,33,63,64 guidelines ideally should incorporate such risk factors; for example, clinicians and patients who would normally consider starting screening at age 50 years for an average-risk woman should consider starting at age 40 for a woman with risk factors placing her at twice average risk.63 However, a better understanding of overdiagnosis is needed to inform how individual characteristics influence the harms of mammography, and breast cancer risk models with better discriminatory accuracy are needed to more accurately individualize information about the benefits and harms of screening. In the meantime, the online Breast Cancer Risk Assessment Tool from the National Cancer Institute can assist physicians and patients in estimating risk.
The significance of the harms of mammography also depends on individuals’ values and preferences, and eliciting these requires provision of accurate and balanced information and values clarification. In light of the harms and modest benefit of screening, as well as the substantial uncertainty surrounding their relative weight for individual patients, clinicians’ efforts must focus on promoting informed screening decisions. The Box offers some suggestions for such discussions.
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Some cancers will be missed, and some women will die of breast cancer regardless of whether they are screened.
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Many cancers will be found, but most women diagnosed with breast cancer will be cured regardless of whether the cancer was found by a mammogram.
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Some cancers that are found would have never caused problems. This is called “overdiagnosis.”
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Often, women are called back for further testing because of an abnormality that is not cancer; this is called a “false-positive” result.
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Studies of the benefits and harms of mammography have limitations and inconsistent results. The numbers reported below are estimates based on what most experts consider the best available evidence, but uncertainty about these estimates remains.
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Mammography decreases the number of women who will die from breast cancer. This benefit is greater for women who are at higher risk for breast cancer based on older age or other risk factors such as family history.
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The number of women whose lives are saved because of mammography varies by age. For every 10 000 women who get regular mammograms for the next 10 years, the number whose lives will be saved because of the mammogram by age group is approximately
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5 of 10 000 women aged 40 to 49 years
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10 of 10 000 women aged 50 to 59 years
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42 of 10 000 women aged 60 to 69 years
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If your breast cancer risk is higher than average, you may benefit more from a mammogram than someone with average risk.
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About half or more of women who have a mammogram yearly for 10 years will have a false-positive mammogram, and up to 20% of these women will need a biopsy. If you do decide to have a mammogram, you can anticipate that you will have at least 1 false-positive finding for which you are called back for additional images and perhaps a biopsy. Most of these findings are false alarms.
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For some women undergoing regular screening, the mammogram may find an invasive cancer or noninvasive condition (ie, ductal carcinoma in situ) that would never have caused problems (“overdiagnosis”). We cannot tell which these are, so they will be treated just like all other cancers. Experts are uncertain of how frequently this happens, but estimates suggest that if a woman undergoing a screening mammogram is diagnosed with cancer or ductal carcinoma in situ, there is about a 19% chance that the cancer is being overdiagnosed, and she will receive unnecessary treatment.
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Experts recommend that women aged 50 to 74 years undergo a screening mammogram every 2 years.
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Whether you are likely to benefit from starting mammograms earlier or having them more frequently depends on your risks for breast cancer and your values and preferences.
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Each woman may feel differently about the possibility of having a false-positive result or being diagnosed with and treated for cancer that might not have caused problems. It is important for you to consider what these experiences might mean for you. It is also important to consider how you might feel if you decide not to undergo screening mammography and you are later diagnosed with breast cancer, even if the likelihood that mammography would have made a difference is small.
Given time constraints in primary care, decision aids may complement the points in the Box, laying the groundwork for discussions between clinicians and patients. Decision aids can facilitate informed decision-making and improve quality of care when there is no clear superior treatment or screening option.82 Limited evidence suggests that decision aids can improve and standardize informed decision-making in breast cancer screening,78,80 but more research is needed to optimize their use and guide integration into practice. One challenge is how best to communicate the evidence.30 Although natural frequencies are preferred, they are derived from absolute risks and require estimating individuals’ baseline risk.76 Research is needed on communicating scientific uncertainty, including regarding overdiagnosis. A recent qualitative study found that the influence of learning about overdiagnosis on screening intentions depended greatly on the magnitude of overdiagnosis presented.83 Expert consensus on overdiagnosis, combined with improved understanding of how to describe this complex issue, may strengthen mammography decision aids. Research will also be needed to explore the long-term effects of decision aids for screening decisions, especially since women with more information may actually be less likely to engage in screening.76,77 Provisions in the Affordable Care Act establishing shared medical decision making as a marker of quality of care could help speed development, dissemination, and evaluation of decision aids.84
This review has provided a broad overview of key considerations in mammography screening decisions and the related areas of uncertainty. It has several limitations. We have relied on evidence of screening benefits from RCTs conducted decades ago in Europe and Canada, which may not generalize to US women today.17,85 Furthermore, reports about overdiagnosis are methodologically heterogeneous and controversial. The review does not address several other important facets of breast cancer screening, including the use of magnetic resonance imaging and newer mammography technologies. It also does not address the complex issue of DCIS.
Although some of the challenges of mammography can be resolved with further research to guide individualized decisions and thoughtful development and dissemination of decision aids, better breast cancer screening tests are needed. More sophisticated tools, for example, could distinguish aggressive vs indolent tumors, reducing the burden of overtreatment.86 Mammography screening appears to be associated with reduced breast cancer mortality, but for some patients, the harms may outweigh the benefits. Until better screening methods are available, improved understanding of these harms, enhanced strategies to identify the highest-risk patients, and tools to help patients and clinicians incorporate these in their decisions should be research priorities.
ARTICLE INFORMATION
Study concept and design: Pace, Keating.
Acquisition, analysis, or interpretation of data: Pace, Keating.
Drafting of the manuscript: Pace, Keating.
Critical revision of the manuscript for important intellectual content: Pace, Keating.
Administrative, technical, or material support: Pace.
Study supervision: Keating.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Keating reported receiving research funding from the National Cancer Institute, the American Cancer Society, and the Komen for the Cure Foundation. Dr Pace reported no disclosures.
Funding/Support: Dr Pace’s work on this review was funded by the Global Women’s Health Fellowship at Brigham and Women’s Hospital.
Role of the Sponsor: The funder played no role in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; the preparation, review, or approval of the manuscript; or the decision to submit the manuscript for publication.
Correction: This article was corrected online April 23, 2014, for an incorrectly reported date.
REFERENCES
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed
PubMed
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
PubMed | Link to Article
Dr Colin Holloway 
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