Breast Cancer Screening
BREAST CANCER SCREENING: THE FACTS
If 2000 women are screened regularly for 10 years:
Of 2000 women (in Europe) who participate in 10 rounds of screening:
Screening can provide false reassurance. Up to 50% of cancers among women in screening programmes are detected between two screening rounds, and these interval cancers are the most dangerous.
Mammography is painful for about a third of women.
The information above is contained in a pamphlet that provides accurate information on the benefits and risks of breast cancer screening and it can be accessed at: www.cochrane.dk/screening/mammography-leaflet.pdf
COCHRANE REVIEW "Screening for breast cancer with mammography" 2013 Issue 6
PC Gotzsche and KJ Jorgensen
PLAIN LANGUAGE SUMMARY
"Screening with mammography uses X-ray imaging to find breast cancer before a lump can be felt. The goal is to treat cancer earlier, when a cure is more likely. The review includes seven trials that involved 6000,000 women in the age range 39 to 74 years who were randomly assigned to receive screening mammograms or not. The studies which provided the most reliable information showed that screening did not reduce breast cancer mortality. Studies that were potentially more biased (less carefully done) found that screening reduced breast cancer mortality. However, screening will result in some women getting a cancer diagnosis even though their cancer would not have led to death or sickness. Currently, it is not possible to tell which women these are, and they are therefore likely to have breasts or lumps removed and to receive radiotherapy unnecessarily. If we assume that screening reduces breast cancer mortality by 15% after 13 years of follow-up and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening through 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings.
Women invited to screening should be fully informed of both the benefits and harms. To help ensure that the requirements for informed choice for women contemplating whether or not to attend a screening programme can be met, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk. Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials. Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening.
The full review can be accessed at:
IMPORTANT ISSUES IN CANCER SCREENING
“Don’t believe in slogans about cancer screening,” warns Peter Gotzsche, Professor of Clinical Research and Analysis and director of the Nordic Cochrane Centre. “They are all wrong, misleading or doubtful.”
For some years Peter Gotzsche kept a folder labelled Dishonesty in breast cancer screening on top of his filing cabinet, storing articles and letters to the editor that contained statements that he knew were dishonest. Eventually he gave up on the idea of writing a paper about this collection, as the number of examples quickly exceeded what could be contained in a single article. He wrote a book instead.
In chapter two of his ground-breaking book Peter Gotzsche describes very clearly and succinctly what the important issues in cancer screening are, and outlines the major scientific disputes surrounding mammography screening. (1)
What it means “to have cancer”
While cancer is a malignant disease that consists of abnormal cells that spread uncontrollably throughout the body, it isn’t always fatal. Yet the public image of cancer is that if left untreated it will kill you. However, recent data suggests that a substantial fraction of detected cancers and precursors of cancer will not prove fatal and will regress. They include cervical cancer, colon cancer, renal cell cancer, melanoma, breast cancer, and neuroblastoma.
Cancer is so common that it is likely that all middle-aged people have cancer somewhere in their body. It is a biological fact of life that we cannot avoid getting cancer as we get older because the telomeres in our DNA, which is like a repair kit that protect us from developing cancer, “runs out of supplies” and cancer cells are then able to develop.
We use the term “having cancer” to mean being ill with cancer, but it means something very different in the context of a screening programme. Because it is possible to detect cancer in virtually everybody over a certain age if we look hard enough, “having cancer” may mean simply having cell changes that will not result in any symptoms or harm us for the rest of our lives. We will die with the cancer but our death is not caused by the cancer we carry. Prostate cancer is one common example of this.
Overdiagnosis and overtreatment
The purpose of screening for a specific cancer is to reduce the mortality rate from that type of cancer. As cancer comprises a group of very different diseases, and many cancers grow very slowly or not at all, one of the important things to know about cancer screening is that it inevitably leads to harm in the form of overdiagnosis and subsequent over-treatment. Overdiagnosis is the detection of a cancer that would not otherwise have been identified clinically during the person’s remaining lifetime.
The problem is that at the moment science cannot distinguish between the harmless cancers that have no symptoms and will not cause any harm and those that are dangerous. So the response to this dilemma is to treat them all. Overdiagnosed breast cancers that would not have caused any problem are treated by surgery, many are treated with radiotherapy, and some with chemotherapy.
As cancer screening always causes harm, it is essential to ensure that the screening being performed does actually reduce mortality from the cancer and whether the reduction is large enough to justify the various harms inflicted on the healthy population that is being screened.
Another important issue in cancer screening is the tendency to over-estimate how accurate the diagnostic tests are. While erroneous diagnoses cause much less harm than overdiagnosis, they are still one of the significant causes of harm that screening results in. Peter Gotzsche notes that this problem has received little attention in the scientific literature and virtually none in the debates about breast cancer screening.
For example, there are two uncertainties involved in deciding whether a woman has breast cancer. They are reading the mammogram and interpreting the biopsy. These result in some women being diagnosed with breast cancer at screening when they do not have breast cancer, yet there are no publications estimating how often women are wrongly diagnosed with breast cancer.
Carcinoma in situ
Carcinoma in situ is another problem. Peter Gotzsche calls it a misnomer. Cancer is an invasive disease whereas carcinoma in situ is Latin and means cancer at the site. It is not invasive: the cell changes remain where they originated.
Issues in cancer epidemiology
There are some essential issues that need to be understood when talking about cancer screening.
The incidence of a disease is the number of new cases occurring in a certain time period, often the calendar year.
The prevalence of a disease is the proportion of a population that has the disease at a given point in time. The prevalence includes all cases, including those that have existed for many years. Like incidence, it is usually expressed per 100,000 people and for a certain age group.
Cancer screening primarily detects slow-growing cancers. This is because the longer the cancer has existed, the greater the chance that it will be picked up at a screening session. In contrast, a cancer that grows very quickly is much more likely to be detected clinically, between two screening sessions. These are referred to as interval cancers and they are therefore more dangerous than cancers detected by screening.
Screening increases the prevalence of cancers with an excellent prognosis due to overdiagnosis, and detects most of the slow-growing cancers. This is why cancers diagnosed in a region with screening will have a more favourable prognosis, on average, than cancers in a region without screening. The screened region has its numbers of breast cancer cases boosted by the many harmless cancers that weren’t detected in the other region because the cancers have no symptoms. This problem is called “length bias.” Overdiagnosis is therefore a special form of length bias.
Another common problem is the bias that occurs in comparing regions with and without screening if researchers use the number of years that patients have survived from their date of diagnosis as the outcome. This is known as “lead-time bias.” The problem can be avoided by comparing the mortality rate of each region or country rather than the years of survival.
Peter Gotzsche states that cancer charities and cancer researchers publish misleading survival analyses so often that it appears like a deliberate strategy to deceive the public into believing that important progress is being made in the fight against cancer.
Breast cancer screening has now become one of the greatest controversies in healthcare today. The general public remains largely unaware of this as media coverage on breast cancer screening chooses to ignore the complex issues as well as the vested interests surrounding breast cancer screening and treatment.
Even more reprehensible is the lack of accurate information given to women by government agencies such as Ministry of Health and the National Screening Unit. It is long past time for the limitations and significant harms of breast cancer screening to be clearly acknowledged so that women are able to make adequately informed decisions before they agree to being screened.
Peter Gotzshe. “Mammography Screening: Truth, Lies and Controversy.” 2012. Published by Radcliffe Publishing Ltd.
Cancer Screening distorts diagnosis of cancer
At the beginning of 2013, leading American cancer scientists called for a set of changes to deal with the problem of over-diagnosis and overtreatment caused by cancer screening.
MORE TROUBLE WITH NZ BREAST CANCER SCREENING
Once again problems have been identified in BreastScreen Aotearoa, New Zealand’s breast cancer screening programme.
An internal audit of initial mammograms by a concerned radiologist working in the Southern DHB’s BreastScreen HealthCare screening programme revealed that there had been a delay in diagnosis for as many as 28 women. The review of 134 mammography films taken between 2007 – 2010 on all women screened by BreastScreen HealthCare and subsequently diagnosed with breast cancer showed that the reading of the mammogram did not flag the existence of a possible malignancy in an unknown percentage of them.
As early signs of breast cancer are notoriously difficult to pickup, normal procedure is for two radiologists to independently examine each mammogram. The Ministry of Health’s chief medical officer, Dr Don Mackie, said on National Radio’s “Nine to Noon” on Thursday 15 March 2012 that the system “wraps around a series of double checks” in the breast cancer screening pathway. (1)
He also explained that regular audits of the breast cancer screening programme don’t look at the problem from this perspective. Regular reviews of performance focus on the interval cancer rate, which is a cancer that develops in the intervals between routine screening. Dr Mackie said that the interval cancer rate for breast cancer screening in New Zealand is comparable with Australia and the UK. However, whether this is true for BreastScreen HealthCare remains to be seen.
A “whole of system review” of BreastScreen HealthCare is now being undertaken, and the Southern District Health Board is contacting the women whose diagnosis was delayed, Dr Mackie said.
A front-page article in the NZ Herald quoted breast surgeon Dr Belinda Scott as saying it was preferable to diagnose breast cancer early rather than late, but “we don’t know whether it makes any difference … or not. Because all cancers are different in their grading and their aggressive- ness, we don’t really know whether you are going to be making a difference to those women diagnosed later.”(2)
An article in the Otago Daily Times on 17 March 2012 raised additional concerns that the problem may be much bigger than first thought. The latest three-year audit of service performance for the three years to November 2011 is still in draft form, but it is believed to have raised concerns of further potential problems. (3)
The MOH is putting together a special team of epidemiologists, radiologists, and screening experts to review the service with the aim of having the team review other mammograms from 2007- 2010. Dr Mackie has admitted that one possible outcome is that a mass rescreening may be required. In the meantime, Counties Manukau DHB and Mid-Central DHB will be providing second reads of mammograms. Two radiologists would also be going to the Southern DHB to perform assessment clinics (when a woman is recalled after a mammogram) indefinitely.
As reported in the December 2011 issue of the AWHC’s newsletter there is considerable controversy internationally over the effectiveness of breast cancer screening, with intense debates about breast cancer screening occurring in the UK and in Scandinavian countries. (4)
In October 2011 the UK announced yet another review of its breast cancer screening programme. Professor Mike Richards, the national cancer director for England, announced in the British Medical Journal that he will lead the review and said he was taking the “current controversy very seriously.” (5)
A review of clinical trials involving a total of 600,000 women concluded it was “not clear whether screening does more good than harm.” It said that for every 2,000 women screened in a 10-year period, one life would be saved, 10 healthy women would have unnecessary treatment and at least 200 women would face psychological distress for many months because of false positive results.
It was acknowledged that “women need more accurate, evidence-based and clear information to be able to make an informed choice about breast screening.” (5)
1. Don Mackie. National Radio “Nine to Noon.’ 15 March 2012.
2. Martin Johnstone. “Breast cancer results delay.” NZ Herald 15 March 2012.
Canadian Medical Association Journal, 22 November 2011
"Time to Stop Mammography Screening?"
The year 2011 has seen the publication of further evidence in the ongoing debate over the benefits and risks of breast cancer screening.
At the end of November 2011 a Canadian Task Force on Preventative Health Care published revised guidelines on breast cancer screening. (1) The recommendations state: in women who are not at high risk
• don’t start routine mammography until age 50
• screen only every two to three years
• stop routine clinical breast examination
• don’t advise women to routinely practice breast self exam.
These recommendations mirror those from the US Preventative Services Taskforce. (2) The US guidelines met with fierce opposition when they were published in 2009, and the Canadian guidelines are already under fire, especially from those with vested interests in breast cancer screening such as the American College of Radiology and the Canadian Association of Radiologists.
As Fiona Godlee, editor of the British Medical Journal commented in her editorial published on 23 November 2011, “The fact that both of these national task forces have reached the same conclusion should give some confidence in the result, but there is no doubting the heat in this controversy.” (3)
Closer to home, an article published online on 29 September 2011 in Breast Cancer Research and Treatment revealed that almost 60% of the Australian decline in breast cancer mortality since 1991 cannot be attributed to BreastScreen, Australia’s free national mammographic programme. The article by Robert Burton and his colleagues, “Adjuvant therapy, not mammographic screening, accounts for most of the observed breast cancer specific mortality reductions in Australian women since the national screening program began in 1991,” claims that most if not all of the reductions can be attributed to the adjuvant hormonal and chemotherapy, which Australian women have increasingly received since 1986. (4)
At the end of the article the authors give a summary of the current evidence found in international studies on the results of breast cancer screening programmes:
“These observations are consistent with the findings in other countries where breast cancer mortality trends have been analysed.
In the UK, where mortality from breast cancer fell by 22, 22 and 12% for women aged 20-49, 50-69 and 70-79 years, respectively between 1987 and 1997, the decreases in mortality were suggested to have mainly resulted from changes in the way that breast cancer was diagnosed and treated.
An examination of age specific falls in breast cancer mortality in the UK between 1989 and 2007 for women aged 40-49 years (41%), 50-64 years (41%) and 65-69 years (38%) lead to the conclusion that mammographic screening did not have a causal role in those falls.
The annual percentage changes in breast cancer mortality in Denmark were examined for 1982 – 2006 and there was no demonstrable effect of the mammographic screening program on breast cancer mortality.
A recent study from Norway reported that mammographic screening could not account for at least two-thirds of the reduction in mortality observed in the first 9 years of the national mammographic screening program in women aged 50-69 years, the age group invited to screen.” (4)
At the recent cancer control conference held in Seoul one of the delegates reported that in the Nordic countries the controversy over the effectiveness of breast cancer screening is very intense and is being widely covered in the media.
The history of New Zealand’s breast cancer screening programme shows that political decisions have often taken precedence and influenced decision-making during its establishment and then in subsequent changes to the programme.
BreastScreen Aotearoa was launched following a politically-driven rushed establishment process in the lead up to the 1996 general election. Nearly a decade later politics once again determined the outcome of the debate over extending the screening programme to women under the age of 50. In 2004 there was considerable controversy about whether Breast Screen Aotearoa should be screening women aged between 40 – 50 years of age. Women’s health groups, health professionals, and the Cancer Society appeared before the Health Select Committee to argue against such an extension.
The National Screening Unit also opposed the extension based on their review of the evidence.
With an election approaching and the usual desperation to appear to be doing something for women, Annette King, Minister of Health at the time, pre-empted the findings of the committee by announcing the extension of screening to women between 45 – 50 years. The Committee’s conclusion, published subsequently, was that the evidence did not support the extension. Once again the breast cancer screening programme was subjected to the whims of NZ’s three-yearly electoral cycle and politics was allowed to trump the evidence.
The latest independent monitoring report of BreastScreen Aotearoa for the two years from January 2008 to December 2009 revealed that one third of all screenings (305,000) are among women aged between 45-49 years (100,000). (5)
Given that studies continue to show that the benefits are small and there is significant potential for harm from mammography for women in this age group, it is obviously time for a review of BreastScreen Aotearoa.